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Page 1: A+ Book

A+ Training & Test Preparation Guide

Volume I – 6th Edition

Specialized Solutions, Inc.

A +

Page 2: A+ Book

Copyright 2003 by Specialized Solutions, Inc.

All rights reserved. Printed in the United States of America. No part of

this book may be used or reproduced in any form or by any means, or stored in a database or retrieval system, without prior written permission of the publisher, except in the case of brief quotations embodied in critical articles and reviews. Making copies of any part of this book for any purpose is a violation of United States copyright laws. For further information, please write to: Publisher, c/o Specialized Solutions, Inc., 338 E. Lemon Street, Tarpon Springs, FL 34689.

ISBN 1-893596-99-1

This book is sold as is, without warranty of any kind, either expressed or implied, respecting the contents of this book, including but not limited to implied warranties for the books quality, performance, merchantability or fitness for any particular purpose. Neither Specialized Solutions, Inc., nor its authorized distributors, shall be liable to the purchaser or any other person or entity with respect to any liability, loss, or damage caused, or alleged to be caused, directly or indirectly by this book. Furthermore, any mention or reference to any products does not constitute an endorsement by Specialized Solutions, Inc.

02 1

Publisher: Specialized Solutions, Inc.

Authors: Garrett Smiley, Richard Harrison

Editor: David Harvey

Trademark Acknowledgments

Brands and product names cited in this manual are trademarks or registered trademarks held by their respective companies. Any use of a term in this book should not be regarded as affecting the validity of any trademark or service mark.

Suggestions/Comments

Please forward all comments or suggestions to:

Specialized Solutions, Inc. 338 E. Lemon Street Tarpon Springs, FL 34689

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Table of Contents

Specialized Solutions, Inc. i

Table of Contents TABLE OF CONTENTS .......................................................................................................... I

ABOUT SPECIALIZED SOLUTIONS ........................................... XIV

INTRODUCTION...............................................................................................................1

CHAPTER 1 – A+ CERTIFICATION .............................................................................3

A+ CERTIFICATION ............................................................................................................3 WHY CERTIFICATION IS IMPORTANT: .................................................................................3 THE A+ EXAM ...................................................................................................................4 A+ CORE HARDWARE EXAM .............................................................................................4

Domain 1: Installation, Configuration, and Upgrading...............................................5 Domain 2: Diagnosing and Troubleshooting .............................................................12 Domain 3: PC Preventive Maintenance, Safety, and Environmental Issues ..............15 Domain 4: Motherboard/Processors/Memory............................................................16 Domain 5: Printers .....................................................................................................20 Domain 6: Basic Networking......................................................................................21

A+ OPERATING SYSTEM TECHNOLOGIES EXAM ..............................................................24 Domain 1: Operating System Fundamentals..............................................................25 Domain 2: Installation, Configuration and Upgrading..............................................29 Domain 3: Diagnosing and Troubleshooting .............................................................32 Domain 4 Networks.....................................................................................................35

SUMMARY........................................................................................................................38 KEYWORDS EXERCISE .................................................................................................39 REVIEW QUESTIONS - CHAPTER 1....................................................................................40

CHAPTER 2 – GENERAL KNOWLEDGE AND TERMS .........................................41

HOW A COMPUTER WORKS..............................................................................................41 THE ROLE OF A COMPUTER SERVICE PROFESSIONAL.......................................................41 CHRONOLOGY OF A COMPUTER .......................................................................................42

The Abacus..................................................................................................................42 The Analytical Engine (A Pre-electronic Computer)..................................................42 The First Electrically-Driven Computer.....................................................................43 The Digital Electronic Computer................................................................................43

THE EVOLUTION OF THE COMPUTER:...............................................................................44 HOW COMPUTERS COMMUNICATE ...................................................................................50

Processing...................................................................................................................50 Input ............................................................................................................................50 Output .........................................................................................................................50 Input, Output and Processing .....................................................................................51

LANGUAGE OF THE COMPUTER ........................................................................................51 The Telegraph and Morse Code .................................................................................52 Parallel and Serial Devices ........................................................................................52

BINARY - THE LANGUAGE OF COMPUTERS (COUNTING BY 2S)........................................53 ASCII ..............................................................................................................................57 COUNTING BY 16 – HEXADECIMAL..................................................................................59 BINARY/DECIMAL/HEXADECIMAL...................................................................................60

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THE COMPUTER BUS ....................................................................................................... 62 Components of a Computer........................................................................................ 63 Processing .................................................................................................................. 63 Input............................................................................................................................ 65 Output......................................................................................................................... 67 Input/Output (I/O) ...................................................................................................... 68 Support Hardware...................................................................................................... 69

CABLING AND CONNECTORS ........................................................................................... 69 Parallel Printer Cables .............................................................................................. 70 Communication Cables .............................................................................................. 71 IEEE 1394 High Performance Serial Bus.................................................................. 71 Cable Pin Assignments............................................................................................... 72 Other Cables Types .................................................................................................... 72

IDENTIFYING CABLES AND CONNECTORS ........................................................................ 74 SUMMARY OF CONNECTORS ............................................................................................ 75 SUMMARY ....................................................................................................................... 77 KEYWORDS EXERCISE................................................................................................. 79 REVIEW QUESTIONS ........................................................................................................ 81

CHAPTER 3- BASIC ELECTRICITY AND SAFETY ............................................... 83

ELECTRICITY REVIEW ..................................................................................................... 83 DIRECT CURRENT (DC)................................................................................................... 84 ALTERNATING CURRENT (AC)........................................................................................ 85 MEASURING ELECTRICITY............................................................................................... 86

The Multimeter ........................................................................................................... 87 TESTING AC POWER ....................................................................................................... 87

Testing AC Outlets with a Multimeter ........................................................................ 87 Testing for AC in DC.................................................................................................. 88 Testing Resistance ...................................................................................................... 89 Testing continuity ....................................................................................................... 89

TESTING A POWER SUPPLY .............................................................................................. 89 ELECTRONIC COMPONENTS ............................................................................................. 90

Capacitors .................................................................................................................. 90 Coils............................................................................................................................ 92 Diodes......................................................................................................................... 92 Fuse ............................................................................................................................ 92 Rectifiers..................................................................................................................... 93 Transformers .............................................................................................................. 93 Transistors.................................................................................................................. 94

STATIC ELECTRICITY AND A COMPUTER ......................................................................... 95 PREVENTING STATIC ELECTRICITY.................................................................................. 95 ELECTRICITY AND SAFETY .............................................................................................. 96 PROTECTION FROM ENVIRONMENTAL HAZARDS ............................................................. 97

Weight......................................................................................................................... 98 Cuts............................................................................................................................. 98 Trip Hazards............................................................................................................... 98

VOLTAGE HAZARDS ........................................................................................................ 98 ESD............................................................................................................................. 99

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Grounds.......................................................................................................................99 High Voltages..............................................................................................................99

FIRE SAFETY ..................................................................................................................100 SUMMARY......................................................................................................................101 KEYWORDS EXERCISE ...............................................................................................102 REVIEW QUESTIONS – CHAPTER 3 .................................................................................103

CHAPTER 4 – MOTHERBOARDS AND PROCESSORS........................................105

XT MOTHERBOARD .......................................................................................................106 AT MOTHERBOARD .......................................................................................................107 BABY AT MOTHERBOARD.............................................................................................107 ATX MOTHERBOARD ....................................................................................................108 MICRO ATX MOTHERBOARD ........................................................................................108 FLEX ATX MOTHERBOARD ...........................................................................................109 LPX MOTHERBOARD.....................................................................................................109 MINI-LPX MOTHERBOARD ...........................................................................................110 NLX MOTHERBOARD ....................................................................................................110 THE COMPUTER CASE ....................................................................................................111

Modified Cases..........................................................................................................112 COMPONENTS ................................................................................................................112 CHIP SET ........................................................................................................................114

ROM – Read Only Memory.......................................................................................115 PROM & Firmware ..................................................................................................115 BIOS..........................................................................................................................116 A typical CMOS setup...............................................................................................119

BIOS CONFIGURATION ..................................................................................................123 THE MOTHERBOARD BATTERY ......................................................................................125 START-UP TEST..............................................................................................................126 BUS ARCHITECTURE ......................................................................................................129 A COMPUTER BUS .........................................................................................................129

An Address Bus .........................................................................................................130 MOTHERBOARD COMPATIBILITY ...................................................................................133 PROCESSOR TECHNOLOGY .............................................................................................133 THE MAIN PROCESSOR ..................................................................................................133

Transistors ................................................................................................................134 Integrated Circuit......................................................................................................134 Microprocessors .......................................................................................................135 Registers....................................................................................................................135 Clock .........................................................................................................................135 Processor Voltages ...................................................................................................136 Processor Mounts .....................................................................................................137 SECC (Single Edge Contact Cartridge) ...................................................................139

SUPPORT FOR THE MAIN PROCESSOR .............................................................................140 DIPP .........................................................................................................................141 PGA...........................................................................................................................141 LCC...........................................................................................................................142 PLCC.........................................................................................................................142 PQFP ........................................................................................................................143

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SECC (Single Edge Contact Cartridge)................................................................... 143 HISTORY OF PROCESSORS.............................................................................................. 143 IN THE BEGINNING ........................................................................................................ 144

The Mainstays........................................................................................................... 145 Virtual Memory ........................................................................................................ 146 Real Mode vs. Protected Mode................................................................................. 146 Limitations................................................................................................................ 146 80386 ........................................................................................................................ 147 80486 ........................................................................................................................ 148

TODAY’S STANDARD ..................................................................................................... 149 Pentium..................................................................................................................... 149 Pentium Pro.............................................................................................................. 151 Pentium II ................................................................................................................. 152 Celeron ..................................................................................................................... 152 Pentium MMX........................................................................................................... 152 Pentium III................................................................................................................ 153 Pentium III Xeon ...................................................................................................... 153 Pentium 4.................................................................................................................. 153 Intel Itanium ............................................................................................................. 155

CO-PROCESSORS ........................................................................................................... 156 NON-INTEL PROCESSORS............................................................................................... 156 INSTALLING A CPU ....................................................................................................... 157

VRM (Voltage Regulator Module) ........................................................................... 157 KEEPING IT COOL!......................................................................................................... 159

Fans .......................................................................................................................... 159 Heat Sinks................................................................................................................. 159 Thermal Compound.................................................................................................. 160 Liquid Cooling.......................................................................................................... 160 Cooling to the Extreme – Liquid Nitrogen!.............................................................. 161

SUMMARY ..................................................................................................................... 162 KEYWORDS EXERCISE............................................................................................... 164 REVIEW QUESTIONS CHAPTER 4.................................................................................... 166

CHAPTER 5 – MEMORY ............................................................................................ 169

RAM & ROM............................................................................................................... 169 Early Memory........................................................................................................... 169

MEMORY TYPES ............................................................................................................ 170 ROM – Ready Only Memory .................................................................................... 170 RAM - Random Access Memory............................................................................... 170

EVERYDAY MEMORY .................................................................................................... 171 DRAM – Chips.......................................................................................................... 171 Matching Memory Modules to Data Bus ................................................................. 174 Reliability of Memory............................................................................................... 175

BEYOND DRAM ........................................................................................................... 176 FPM.......................................................................................................................... 176 EDO RAM................................................................................................................. 176 SDRAM..................................................................................................................... 177 DDR SDRAM............................................................................................................ 177

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DRDRAM ..................................................................................................................177 Synclink Dynamic RAM ............................................................................................178

SPECIAL RAM ...............................................................................................................178 Caching .....................................................................................................................178

WORKING WITH MEMORY..............................................................................................179 SIPPs.........................................................................................................................180 SIMMs.......................................................................................................................180 72-pin SIMM .............................................................................................................181 DIMMs ......................................................................................................................181 RIMMs.......................................................................................................................182 Installing Memory.....................................................................................................182 Handling Memory Problems.....................................................................................184 Logical Memory ........................................................................................................185

EMS – EXPANDED MEMORY SYSTEM ...........................................................................186 EXTENDED MEMORY .....................................................................................................187 OPTIMIZING MEMORY....................................................................................................188 SUMMARY......................................................................................................................191 KEYWORDS EXERCISE ...............................................................................................192 REVIEW QUESTIONS CHAPTER 5 ....................................................................................193

CHAPTER 6 – POWER SUPPLIES.............................................................................195

MATCHING SIZE TO CASE ..............................................................................................195 How much power is enough?....................................................................................196

GETTING CONNECTED....................................................................................................196 P8 & P9.....................................................................................................................197 Molex or mini............................................................................................................199 Power Switch Connectors .........................................................................................200

WHEN THINGS GO WRONG! ............................................................................................200 The Power Company.................................................................................................201

THE POWER SUPPLY ......................................................................................................203 SUMMARY......................................................................................................................204 KEYWORDS EXERCISE ...............................................................................................205 REVIEW QUESTIONS CHAPTER 6 ....................................................................................206

CHAPTER 7 – STORAGE DEVICES..........................................................................207

PUNCH CARDS AND TAPE DRIVES..................................................................................207 Installation ................................................................................................................208

FLOPPY DRIVES .............................................................................................................208 Floppy Disk Drive Basics .........................................................................................208 Installation ................................................................................................................210 Maintaining a Floppy Drive .....................................................................................212 Troubleshooting a Floppy.........................................................................................212

HARD DRIVES ................................................................................................................215 Technology of Hard Drives.......................................................................................215 Read/Write Heads .....................................................................................................216 Magnetically Storing Data........................................................................................217 Hard Disk Architecture.............................................................................................218 Cylinders ...................................................................................................................219

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Heads........................................................................................................................ 220 Landing Zone............................................................................................................ 220 Sectors ...................................................................................................................... 220 Write Precomp.......................................................................................................... 221

CALCULATING THE SIZE OF A DRIVE ............................................................................. 221 Hard Drive Types ..................................................................................................... 222

HARD DRIVE INTERFACES ............................................................................................. 223 ST506/412................................................................................................................. 223 ESDI ......................................................................................................................... 224 IDE ........................................................................................................................... 224 ATA........................................................................................................................... 225 ATA-2 (Fast ATA/Enhanced IDE [EIDE])............................................................... 225 ATA-3........................................................................................................................ 225 ATA-4 (Ultra-DMA/ATA-33/DMA 33)..................................................................... 225 ATA-5 (ATA/66 / Ultra DMA/66 / Fast ATA-2) ....................................................... 225 Ultra-ATA 100 (Ultra ATA DMA Mode 5)............................................................... 225 EIDE......................................................................................................................... 225 SCSI .......................................................................................................................... 226

INSTALLATION AND SET-UP OF A HARD DRIVE ............................................................. 226 Installation Procedure.............................................................................................. 226 Physical Installation................................................................................................. 227 CMOS and Hard Drives ........................................................................................... 228 Low-Level Formatting.............................................................................................. 230 Bootable Disk ........................................................................................................... 230 Partitioning .............................................................................................................. 231 How the File Allocation Table Works ...................................................................... 232 Sectors and Clusters................................................................................................. 233 Naming of Partitions ................................................................................................ 234 How to Partition a Hard Drive ................................................................................ 235 High-Level Formatting............................................................................................. 237

MAINTAINING A HARD DRIVE ....................................................................................... 237 Microsoft to the Rescue ............................................................................................ 237 When all else fails..................................................................................................... 238

HARD DRIVE PROBLEMS ............................................................................................... 239 High Capacity Hard Drives ..................................................................................... 239 Limitations of Early Drives ...................................................................................... 239 Increasing Capacity ................................................................................................. 240 Increasing Data Transfer Speeds ............................................................................. 241

INSTALLING EIDE DRIVES ............................................................................................ 241 Enable Secondary Controllers ................................................................................. 241 Set the Enhanced BIOS............................................................................................. 242 Setting Programmed I/O Mode ................................................................................ 242

SCSI DRIVES................................................................................................................. 242 Installing SCSI.......................................................................................................... 243 Rule #1 – Terminate ................................................................................................. 244 Methods of Terminating: .......................................................................................... 244 Rule # 2 – Set the ID................................................................................................. 244 Rule # 3 – Set the Logical Unit Numbers (LUN)...................................................... 245

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SCSI Standards .........................................................................................................245 Single-ended SCSI (SE) vs. High Voltage Differential SCSI (HVD) ........................246 Low-Voltage Differential SCSI (LVD) ......................................................................246 SCSI-1 and SCSI-2....................................................................................................247 SCSI-3 .......................................................................................................................248 Fiber Channel SCSI ..................................................................................................248 SCSI cabling..............................................................................................................251 SCSI Drivers .............................................................................................................251 Advantages of SCSI...................................................................................................251 RAID 0 ......................................................................................................................252 RAID 1 ......................................................................................................................252 RAID 2 ......................................................................................................................252 RAID 3 ......................................................................................................................252 RAID 4 ......................................................................................................................253 RAID 5 ......................................................................................................................253 RAID 6 ......................................................................................................................253

USB DRIVES..................................................................................................................253 OPTICAL DRIVES............................................................................................................254

CD-ROMs .................................................................................................................254 CD TECHNOLOGY..........................................................................................................255

Storing Data..............................................................................................................255 Connections...............................................................................................................255 Audio Capability .......................................................................................................256 Speed and Access Time .............................................................................................256 Recordable CD (CD-R).............................................................................................257 CD-R Encoding.........................................................................................................257 CD-R Compatibility with CD-ROM..........................................................................258 CD-R Software..........................................................................................................258 CD-R Drives..............................................................................................................258 ReWritable CD (CD-RW) .........................................................................................258 CD-RW Encoding......................................................................................................258 Installing a CD-ROM................................................................................................259 Controller Cards.......................................................................................................259 Installing in the Computer ........................................................................................260

SOFTWARE SET-UP ........................................................................................................260 Windows 3.x ..............................................................................................................261 Windows 9x ...............................................................................................................261

MAINTAINING A CD-ROM ............................................................................................262 MULTIMEDIA .................................................................................................................262

Video Capture Software............................................................................................263 Other Optical Drives.................................................................................................264 WORM (Write Once-Read Many).............................................................................264 Digital Versatile/Video Disk (DVD) .........................................................................264 Rewritable Optical ....................................................................................................265

SUMMARY......................................................................................................................266 KEYWORDS EXERCISE ...............................................................................................268 REVIEW QUESTIONS CHAPTER 7 ....................................................................................271

CHAPTER 8 – BUSES ...................................................................................................275

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EXPANSION BUSES ........................................................................................................ 275 Bus Functions ........................................................................................................... 275 Development of the Expansion Bus .......................................................................... 276 ISA (Industry Standard Architecture)....................................................................... 276 MCA (Micro Channel Architecture)......................................................................... 277 EISA (Enhanced Industry Standard Architecture) ................................................... 278

LOCAL BUSES................................................................................................................ 278 VESA (VL-Bus) ......................................................................................................... 279 PCI............................................................................................................................ 280 PCI 2.2...................................................................................................................... 280 PCI Expansion Slots................................................................................................. 280 USB........................................................................................................................... 281

USB 2.0 ........................................................................................................................ 282 FireWire (IEEE-1394).............................................................................................. 282 AMR (Audio/Modem Riser) ...................................................................................... 282 CNR (Communications and Networking Riser) ....................................................... 282 AGP (Accelerated Graphics Port) ........................................................................... 283 Configuring Expansion Cards.................................................................................. 284

ADDRESSING – WHERE IS THAT CARD? ......................................................................... 284 INTERRUPTING – WHO’S TURN TO TALK? ..................................................................... 286

8-bit bus.................................................................................................................... 287 16-bit bus.................................................................................................................. 287 Configuring IRQs ..................................................................................................... 289 IRQ Conflicts............................................................................................................ 290 DMA Channels ......................................................................................................... 290

ASSIGNING RESOURCES THROUGH PORTS ..................................................................... 291 Conflicts with PORTS............................................................................................... 292

INSTALLING AN EXPANSION CARD ................................................................................ 292 SUMMARY ..................................................................................................................... 294 KEYWORDS EXERCISE............................................................................................... 295 REVIEW QUESTIONS CHAPTER 8.................................................................................... 296

CHAPTER 9 – DISASSEMBLY, REASSEMBLY, AND UPGRADING................. 299

DISASSEMBLY AND RE-ASSEMBLY OF A COMPUTER...................................................... 299 Preparation .............................................................................................................. 299 Documentation to collect before starting the job:.................................................... 299 Questions to ask yourself before starting the job:.................................................... 300

TOOL KIT ...................................................................................................................... 300 Software: .................................................................................................................. 301 Software Utilities:..................................................................................................... 302

DISASSEMBLY ............................................................................................................... 302 RE-ASSEMBLY ............................................................................................................... 303 UPGRADING A COMPUTER ............................................................................................. 303

The Number One Question!...................................................................................... 304 CPU Upgrades ......................................................................................................... 305 Expansion Cards ...................................................................................................... 306 Drives ....................................................................................................................... 309 Motherboards ........................................................................................................... 311

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SUMMARY......................................................................................................................314 KEYWORDS EXERCISE ...............................................................................................315 REVIEW QUESTIONS CHAPTER 9 ....................................................................................316

CHAPTER 10 – PRINTERS..........................................................................................319

PRINTER BASICS ............................................................................................................319 PRINTER TECHNOLOGY ..................................................................................................321

Impact Printers .........................................................................................................321 Dot Matrix Printers...................................................................................................322 Daisy Wheel Printers ................................................................................................323 Thermal Printers.......................................................................................................323 Thermal Wax Transfer Printer..................................................................................324 Dye Sublimation Printers..........................................................................................325 Ink Jet Printers..........................................................................................................325 Laser Printers ...........................................................................................................326 Laser Printer Sub-System – Toner Cartridge ...........................................................327 Photosensitive Drum.................................................................................................327 Primary Corona........................................................................................................327 Toner .........................................................................................................................328 Developer roller........................................................................................................328 Cleaner blade............................................................................................................328 Laser Printer Sub-System – Laser Scanning Assembly ............................................328 Laser Printer Sub-System – Power Supply ...............................................................328 High-Voltage Power Supply (HVPS) ........................................................................328 DC Power Supply (DCPS) ........................................................................................328 Laser Printer Sub-System – Paper Transport Assembly ..........................................328 Laser Printer Sub-System – Transfer Corona Assembly ..........................................329 Laser Printer Sub-System – Printer Controller Assembly........................................329 The Laser Printing Process ......................................................................................329 Condition the Drum ..................................................................................................330 Write the Image.........................................................................................................330 Transfer Toner ..........................................................................................................331 Transfer –Image to Paper.........................................................................................331 Fuse the Image..........................................................................................................331 Clean the Drum.........................................................................................................331 When Laser Printers don’t work: .............................................................................332 Solid Ink Printers ......................................................................................................333

PRINTER IMAGE CONCEPTS ............................................................................................335 Character vs. Raster .................................................................................................335 Resolution .................................................................................................................335 High Quality Printing ...............................................................................................336 Computer to Printer Communication .......................................................................336 PCL – Printer Control Language .............................................................................336 PostScript..................................................................................................................337

MULTIFUNCTION PRINTERS............................................................................................337 PLOTTERS ......................................................................................................................337 PRINTER ACCESSORIES ..................................................................................................338

Internal Print Servers ...............................................................................................338

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Post Script Upgrade Software.................................................................................. 338 Duplexer ................................................................................................................... 338 Paper tray................................................................................................................. 339 Memory..................................................................................................................... 339 Sheet Stacker ............................................................................................................ 339 External Printer Server ............................................................................................ 340 Folding Machines..................................................................................................... 340 Printer Hard Drives ................................................................................................. 340 Staplers..................................................................................................................... 341 Network Cards.......................................................................................................... 341 Automatic Document Feeder.................................................................................... 341

PRINTER INSTALLATION ................................................................................................ 342 SUMMARY ..................................................................................................................... 343 KEYWORDS EXERCISE............................................................................................... 344 REVIEW QUESTIONS CHAPTER 10.................................................................................. 346

CHAPTER 11 – MONITORS ....................................................................................... 347

DISPLAYS ...................................................................................................................... 347 Display Technology.................................................................................................. 347 Monitor Technology ................................................................................................. 347 CRT........................................................................................................................... 347 Persistence vs. Scanning Frequency ........................................................................ 348 Sweeping and Refresh Rates..................................................................................... 349 Interlacing ................................................................................................................ 349 Thin CRTs................................................................................................................. 350 LCD Displays ........................................................................................................... 350 Gas Plasma Displays................................................................................................ 350 Image Technology .................................................................................................... 350 Green Monitor .......................................................................................................... 355 Display Adjustment................................................................................................... 355 When a monitor goes bad......................................................................................... 357

VIDEO DISPLAY ADAPTERS ........................................................................................... 358 Displays and Memory............................................................................................... 359 VRAM ....................................................................................................................... 360 WRAM ...................................................................................................................... 361 MDRAM.................................................................................................................... 361 SGRAM..................................................................................................................... 361 EDO.......................................................................................................................... 361 Un-accelerated vs. Accelerated Video Cards........................................................... 361 Accelerated Graphics Port (AGP) ........................................................................... 361 Adapter Troubleshooting and Maintenance............................................................. 362

SUMMARY ..................................................................................................................... 363 KEYWORDS EXERCISE............................................................................................... 364 REVIEW QUESTIONS CHAPTER 11.................................................................................. 366

CHAPTER 12 – MODEMS ........................................................................................... 367

MODEM BASICS............................................................................................................. 367 COMMUNICATION .......................................................................................................... 369

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Serial/Parallel Conversion .......................................................................................370 DIGITAL COMMUNICATION ............................................................................................371

Synchronous Communication ...................................................................................371 Asynchronous Communication .................................................................................371 Parity.........................................................................................................................372 Modem Hardware .....................................................................................................372 Telephone Lines ........................................................................................................373

MODEM INSTALLATION..................................................................................................374 Modem Card .............................................................................................................374 External Modem........................................................................................................375 Modem Speeds ..........................................................................................................375 Bits per Second (bps) ................................................................................................376 Fax/Modems..............................................................................................................376

INFORMATION TRANSFER PROTOCOLS ...........................................................................376 Hardware Protocols..................................................................................................377 Software Flow Control..............................................................................................377 Data Compression Protocols....................................................................................377 Error Correction Protocols ......................................................................................377

ESTABLISHING A CONNECTION ......................................................................................378 Modem Standards .....................................................................................................378 Modulation Standards...............................................................................................379 Data Transmission Standards...................................................................................379 MNP Standards.........................................................................................................379 Today’s Modem Standards .......................................................................................379

56K MODEMS ................................................................................................................380 AT COMMANDS .............................................................................................................381 TROUBLESHOOTING .......................................................................................................382 SUMMARY......................................................................................................................384 KEYWORDS EXERCISE ...............................................................................................385 REVIEW QUESTIONS CHAPTER 12 ..................................................................................387

CHAPTER 13 – PORTABLE SYSTEMS ....................................................................389

TYPES OF PORTABLES ....................................................................................................389 Laptops......................................................................................................................389 Notebooks..................................................................................................................389 Sub-Notebooks (Palmtops)........................................................................................390 Personal Digital Assistants (PDA) ...........................................................................390

COMPUTER CARDS (PCMCIA) ......................................................................................391 PORTABLE COMPUTER HARDWARE ...............................................................................392

Displays.....................................................................................................................392 Processors.................................................................................................................394 Voltage Reduction.....................................................................................................394 Memory .....................................................................................................................395 Hard Disk Drives ......................................................................................................395 Removable Media......................................................................................................396 Infrared Ports............................................................................................................396 Keyboards .................................................................................................................396 Pointing Devices .......................................................................................................396

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Batteries.................................................................................................................... 397 New Technology ....................................................................................................... 398 Power Management.................................................................................................. 399

SUMMARY ..................................................................................................................... 400 KEYWORDS EXERCISE............................................................................................... 401 REVIEW QUESTIONS CHAPTER 13.................................................................................. 402

CHAPTER 14 – NETWORKING................................................................................. 403

NETWORKS .................................................................................................................... 403 Basic Requirements of a Network ............................................................................ 403 Networking ............................................................................................................... 404 LAN........................................................................................................................... 404 WAN.......................................................................................................................... 405 Types of Networks .................................................................................................... 405

NETWORK TOPOLOGY ................................................................................................... 406 WIRELESS NETWORKS ................................................................................................... 407

Why Wireless? .......................................................................................................... 407 Wireless Transmission Methods............................................................................... 408 Radio Transmission.................................................................................................. 409 Satellite Station Networking..................................................................................... 410

NETWORK OPERATING SYSTEM (NOS) ......................................................................... 411 NETWORK INTERFACE CARDS (LAN ADAPTER) ............................................................ 411

Installing a NIC........................................................................................................ 411 NETWORK CABLING ...................................................................................................... 413

Twisted pair.............................................................................................................. 413 Coaxial Cable........................................................................................................... 415 Coaxial Connectors.................................................................................................. 416 Fiber Optic ............................................................................................................... 419 Null-modem Cable.................................................................................................... 420 Cross-over Cable...................................................................................................... 420 Straight-through Cable............................................................................................. 421

SPECIFYING THE RIGHT CABLE...................................................................................... 421 LAN COMMUNICATION – ACCESS METHODS ............................................................... 422

CSMA/CD (Carrier-Sense Multiple Access with Collision Detection) .................... 422 CSMA/CA (Carrier-Sense Multiple Access with Collision Avoidance) ................... 423 Token Passing........................................................................................................... 423 Demand Priority....................................................................................................... 424

NETWORK PROTOCOLS .................................................................................................. 424 EXTENDING A LAN ....................................................................................................... 425 MAINTAINING AND TROUBLESHOOTING NETWORKS ..................................................... 426 NETWORK CERTIFICATION ............................................................................................ 428

Network+.................................................................................................................. 428 i-Net+ ....................................................................................................................... 428 Microsoft MCP......................................................................................................... 428 Microsoft MCSE....................................................................................................... 429

THE INTERNET............................................................................................................... 429 Internet Basics .......................................................................................................... 429 Domain ..................................................................................................................... 431

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Domain Name Server................................................................................................431 INTERNET JARGON .........................................................................................................432 GETTING CONNECTED....................................................................................................436 SUMMARY......................................................................................................................437 KEYWORDS EXERCISE ...............................................................................................438 REVIEW QUESTIONS CHAPTER 14 ..................................................................................443

CHAPTER 15 – PREVENTIVE MAINTENANCE ....................................................445

MATERIALS FOR PREVENTIVE MAINTENANCE ...............................................................445 GENERAL PREVENTIVE MAINTENANCE..........................................................................447

Monitors....................................................................................................................447 Hard Disk Drives ......................................................................................................448 Floppy Disk Drives ...................................................................................................448 Keyboard and Mouse ................................................................................................449 Printers .....................................................................................................................449 PM Schedule .............................................................................................................451

ENVIRONMENTALLY SAFE DISPOSAL OF COMPONENTS .................................................452 SUMMARY......................................................................................................................453 KEYWORDS EXERCISE ...............................................................................................454 REVIEW QUESTIONS CHAPTER 15 ..................................................................................455

CONCLUSION ...............................................................................................................457

APPENDIX A – HOW TO REGISTER FOR THE A+ EXAM.................................459

TO REGISTER FOR THE A+ EXAM...................................................................................459

APPENDIX B – TABLES ..............................................................................................461

APPENDIX C – GLOSSARY........................................................................................485

APPENDIX D – REVIEW QUESTIONS AND ANSWERS ......................................521

CHAPTER 1 – A+ CERTIFICATION ..................................................................................521 CHAPTER 2 – GENERAL KNOWLEDGE AND TERMS ........................................................522 CHAPTER 3 – BASIC ELECTRICITY AND SAFETY ............................................................525 CHAPTER 4 – MOTHERBOARDS AND PROCESSORS .........................................................528 CHAPTER 5 – MEMORY..................................................................................................531 CHAPTER 6 – POWER SUPPLIES......................................................................................533 CHAPTER 7 – STORAGE DEVICES ...................................................................................535 CHAPTER 8 – INSTALLING PERIPHERALS .......................................................................540 CHAPTER 9 – DISASSEMBLY, REASSEMBLY AND UPGRADING .......................................544 CHAPTER 10 – PRINTERS................................................................................................547 CHAPTER 11 – MONITORS .............................................................................................549 CHAPTER 12 – MODEMS ................................................................................................551 CHAPTER 13 – PORTABLE SYSTEMS ..............................................................................553 CHAPTER 14 – NETWORKING.........................................................................................556 CHAPTER 15 – PREVENTIVE MAINTENANCE ..................................................................560

INDEX..............................................................................................................................561

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About SPECIALIZED SOLUTIONS Welcome to Specialized Solutions, Inc. A+ training and certification course. We thank you for choosing our company as your resource for Information Technology Self-Study Training.

SPECIALIZED SOLUTIONS is dedicated to providing the computer professional the highest level of self-study training and certification materials the industry has to offer. We are committed to always be on the leading edge of new computer environment training products.

We will always provide a quality product to customers at a price that is within reach of most computer professionals. We strive to provide training programs that far exceed the expectations of our customers. One hundred percent customer satisfaction and unmatched customer service is always our commitment to the computer professional.

Our highly skilled staff of computer and educational professionals is dedicated to delivering high quality, cost-effective programs that are customized to suit your needs.

To see other course offerings, please visit us at:

http://www.specializedsolutions.com/

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Introduction

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Introduction

This Training Guide is designed to meet all of the A+ exam objectives. It can be used in conjunction with the Specialized Solutions, Inc. A+ video training series, as a stand-alone textbook, or as a textbook in a classroom environment. We have carefully prepared this multi-media training material to provide you with the needed information in a logical, easy to follow format.

Our staff consists of Microsoft Certified Professionals, Technical Writers, Technical Editors, Computer Graphics Experts, and Digital Video Studio Professionals. We hope you enjoy your A+ training program. Remember, at Specialized Solutions, our success is directly tied to the success our students have with our training programs. We are here to help with all of your training and certification needs!

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Chapter 1 – A+ Certification

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Chapter 1 – A+ Certification

Certification is the first step in establishing your presence as a PC Professional. It will provide the skills you need, establish your knowledge base and give you the confidence to get you started. This chapter discusses the A+ Exam, what it is, and how to take it.

A+ Certification

A+ Certification is a testing program sponsored by the Computing Technology Industry Association (CompTIA) that certifies the competency of service technicians in the computer industry. Major computer hardware and software manufacturers, vendors, distributors, resellers, and publications back the program.

Earning A+ certification means that you possess the knowledge, skills and customer relation skills essential for a successful computer service technician. The exams cover a broad range of hardware and software technologies, but are not related to any vendor-specific products.

Why certification is important:

There are two primary reasons that A+ certification is important. The first is to verify past experience and achievement. The second is to launch a new career or vocation. In either case, there are many benefits of being A+ Certified.

• Recognized proof of professional achievement. The A+ credential validates that the holder has reached a level of competence commonly accepted and valued by the industry.

• Enhanced job opportunities. Many employers give preference in hiring applicants with A+ Certification. Some employers require A+ as a condition of employment.

• Opportunity for advancement. The A+ credential can be a plus when an employer awards job promotions.

• Training requirement. A+ Certification is being adopted as a prerequisite to attending certain vendor training courses. Vendors find they can cut their training programs by as much as 50% by requiring that all attendees are A+ certified.

• Customer confidence. As the public learns about A+ Certification, customers will require that only certified technicians be assigned to their accounts.

• Companies benefit from improved productivity. Certified employees perform work faster and more accurately. Statistics show certified employees can work up to 75% faster than non-certified employees can work.

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• Customer satisfaction. When employees have credentials that prove their competency, customer expectations are more likely to be met. More business can be generated for the employer through repeat sales to satisfied customers.

The A+ Exam

To become certified, you must pass two test modules - the A+ Hardware Core Exam and the A+ Operating System (OS) Technologies Exam. The tests are administered by Prometric and VUE (they each have hundreds of authorized testing centers in any of the 50 states nationwide and in 150+ other countries worldwide. To register for the test call: 1-800-77-MICRO (1-800-776-4276) for Prometric or visit their Web site at www.2test.com, or call VUE at 952-995-8758 or visit their Web site at www.vue.com. This text focuses on meeting the requirements for these examinations.

A+ Core Hardware Exam

This examination measures essential competencies for a microcomputer hardware service technician with six months of on-the-job experience. It is broken down into six sections (called Domains). The following table lists the domains and the extent to which they are represented.

Core Exam

Domain % Of Examination

1.0 – Installation, Configuration, and Upgrading 30%

2.0 – Diagnosing and Troubleshooting 30%

3.0 – Preventive Maintenance 5%

4.0 – Motherboard/Processors/Memory 15%

5.0 – Printers 10%

6.0 – Basic Networking 10%

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Domain 1: Installation, Configuration, and Upgrading

1.1 Identify the names, purpose, and characteristics, of system modules. Recognize these modules by sight or definition. Examples of concepts and modules are:

• Motherboard

• Firmware

• Power supply

• Processor /CPU

• Memory

• Storage devices

• Display devices

• Adapter cards

• Ports

• Cases

• Riser cards

1.2 Identify basic procedures for adding and removing field replaceable modules for desktop systems. Given a replacement scenario, choose the appropriate sequences.

Desktop components:

• Motherboard

• Storage device

o FDD

o HDD

o CD/CDRW

o DVD/DVDRW

o Tape drive

o Removable storage

• Power supply

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o AC adapter

o AT/ATX

• Cooling systems

o Fans

o Heat sinks

o Liquid cooling

• Processor /CPU

• Memory

• Display device

• Input devices

o Keyboard

o Mouse/pointer devices

o Touch screen

• Adapters

o Network Interface Card (NIC)

o Sound card

o Video card

o Modem

o SCSI

o IEEE 1394/Firewire

o USB

o Wireless

1.3 Identify basic procedures for adding and removing field-replaceable modules for portable systems. Given a replacement scenario, choose the appropriate sequences.

Portable components:

• Storage devices

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o FDD

o HDD

o CD/CDRW

o DVD/DVDRW

o Removable storage

• Power sources

o AC adapter

o DC adapter

o Battery

• Memory

• Input devices

o Keyboard

o Mouse/pointer devices

o Touch screen

• PCMCIA/Mini PCI Adapters

o Network Interface Card (NIC)

o Modem

o SCSI

o IEEE 1394/Firewire

o USB

o Storage (memory and hard drive)

• Docking station/port replicators

• LCD panel

• Wireless

o Adapter/controller

o Antennae

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1.4 Identify typical IRQs, DMAs, and I/O addresses, and procedures for altering these settings when installing and configuring devices. Choose the appropriate installation or configuration steps in a given scenario.

Content may include the following:

• Legacy devices (e.g., ISA sound card)

• Specialized devices (e.g., CAD/CAM)

• Internal modems

• Floppy drive controllers

• Hard drive controllers

• Multimedia devices

• NICs

• I/O ports

o Serial

o Parallel

o USB ports

o IEEE 1394/Firewire

o Infrared

1.5 Identify the names, purposes, and performance characteristics, of standardized / common peripheral ports, associated cabling, and their connectors. Recognize ports, cabling, and connectors, by sight.

Content may include the following:

• Port types

o Serial

o Parallel

o USB ports

o IEEE 1394/Firewire

o Infrared

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• Cable types

o Serial (Straight through vs. null modem)

o Parallel

o USB

• Connector types

o Serial

§ DB-9

§ DB-25

§ RJ-11

§ RJ-45

o Parallel

§ DB-25

§ Centronics (mini, 36)

• PS2/MINI-DIN

• USB

• IEEE 1394

1.6 Identify proper procedures for installing and configuring common IDE devices. Choose the appropriate installation or configuration sequences in given scenarios. Recognize the associated cables.

Content may include the following:

• IDE Interface Types

o EIDE

o ATA/ATAPI

o Serial ATA

o PIO

• RAID (0, 1 and 5)

• Master/Slave/cable select

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• Devices per channel

• Primary/Secondary

• Cable orientation/requirements

1.7 Identify proper procedures for installing and configuring common SCSI devices. Choose the appropriate installation or configuration sequences in given scenarios. Recognize the associated cables.

Content may include the following:

• SCSI Interface Types

o Narrow

o Fast

o Wide

o Ultra-wide

o LVD

o HVD

• Internal versus external

• SCSI IDs

o Jumper block/DIP switch settings (binary equivalents)

o Resolving ID conflicts

• RAID (0, 1 and 5)

• Cabling

o Length

o Type

o Termination requirements (active, passive, auto)

1.8 Identify proper procedures for installing and configuring common peripheral devices. Choose the appropriate installation or configuration sequences in given scenarios.

Content may include the following:

• Modems and transceivers (dial-up, cable, DSL, ISDN)

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• External storage

• Digital cameras

• PDAs

• Wireless access points

• Infrared devices

• Printers

• UPS (Uninterruptible Power Supply) and suppressors

• Monitors

1.9 Identify procedures to optimize PC operations in specific situations. Predict the effects of specific procedures under given scenarios.

Topics may include:

• Cooling systems

o Liquid

o Air

o Heat sink

o Thermal compound

• Disk subsystem enhancements

o Hard drives

o Controller cards (e.g., RAID, ATA-100, etc.)

o Cables

• NICs

• Specialized video cards

• Memory

• Additional processors

1.10 Determine the issues that must be considered when upgrading a PC. In a given scenario, determine when and how to upgrade system components.

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Issues may include:

• Drivers for legacy devices

• Bus types and characteristics

• Cache in relationship to motherboards

• Memory capacity and characteristics

• Processor speed and compatibility

• Hard drive capacity and characteristics

• System/firmware limitations

• Power supply output capacity

Components may include the following:

• Motherboards

• Memory

• Hard drives

• CPU

• BIOS

• Adapter cards

• Laptop power sources

o Lithium ion

o NiMH

o Fuel cell

• PCMCIA Type I, II, III cards

Domain 2: Diagnosing and Troubleshooting

2.1 Recognize common problems associated with each module and their symptoms, and identify steps to isolate and troubleshoot the problems. Given a problem situation, interpret the symptoms and infer the most likely cause.

Content may include the following:

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• I/O ports and cables

o Serial

o Parallel

o USB ports

o IEEE 1394/Firewire

o Infrared

o SCSI

• Motherboards

o CMOS/ BIOS settings

o POST audible/visual error codes

• Peripherals

• Computer case

o Power supply

o Slot covers

o Front cover alignment

• Storage devices and cables

o FDD

o HDD

o CD/CDRW

o DVD/DVDRW

o Tape drive

o Removable storage

• Cooling systems

o Fans

o Heat sinks

o Liquid cooling

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o Temperature sensors

• Processor /CPU

• Memory

• Display device

• Input devices

o Keyboard

o Mouse/pointer devices

o Touch screen

• Adapters

o Network Interface Card (NIC)

o Sound card

o Video card

o Modem

o SCSI

o IEEE 1394/Firewire

o USB

• Portable Systems

o PCMCIA

o Batteries

o Docking Stations/Port Replicators

o Portable unique storage

2.2 Identify basic troubleshooting procedures and tools, and how to elicit problem symptoms from customers. Justify asking particular questions in a given scenario.

Content may include the following:

• Troubleshooting/isolation/problem determination procedures

• Determining whether a hardware or software problem

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• Gathering information from user

o Customer Environment

o Symptoms/Error Codes

o Situation when the problem occurred

Domain 3: PC Preventive Maintenance, Safety, and Environmental Issues

3.1 Identify the various types of preventive maintenance measures, products and procedures and when and how to use them.

Content may include the following:

• Liquid cleaning compounds

• Types of materials to clean contacts and connections

• Non-static vacuums (chassis, power supplies, fans)

• Cleaning monitors

• Cleaning removable media devices

• Ventilation, dust, and moisture control on the PC hardware interior.

• Hard disk maintenance (defragging, scan disk, CHKDSK)

• Verifying UPS (Uninterruptible Power Supply) and suppressors

3.2 Identify various safety measures and procedures, and when/how to use them.

Content may include the following:

• ESD (Electrostatic Discharge) precautions and procedures

o What ESD can do, how it may be apparent, or hidden

o Common ESD protection devices

o Situations that could present a danger or hazard

• Potential hazards and proper safety procedures relating to

o High-voltage equipment

o Power supply

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o CRTs

3.3 Identify environmental protection measures and procedures, and when/how to use them.

Content may include the following:

• Special disposal procedures that comply with environmental guidelines.

• Batteries

• CRTs

• Chemical solvents and cans

• MSDS (Material Safety Data Sheet)

Domain 4: Motherboard/Processors/Memory

4.1 Distinguish between the popular CPU chips in terms of their basic characteristics.

Content may include the following:

• Popular CPU chips (Pentium class compatible)

• Voltage

• Speeds (actual vs. advertised)

• Cache level I, II, III

• Sockets/slots

• VRM(s)

4.2 Identify the types of RAM (Random Access Memory), form factors, and operational characteristics. Determine banking and speed requirements under given scenarios.

Content may include the following:

• Types

o EDO RAM (Extended Data Output RAM)

o DRAM (Dynamic Random Access Memory)

o SRAM (Static RAM)

o VRAM (Video RAM)

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o SDRAM (Synchronous Dynamic RAM)

o DDR (Double Data Rate)

o RAMBUS

• Form factors (including pin count)

o SIMM (Single In-line Memory Module)

o DIMM (Dual In-line Memory Module)

o SoDIMM (Small outline DIMM)

o MicroDIMM

o RIMM (Rambus Inline Memory Module)

• Operational characteristics

o Memory chips (8-bit, 16-bit, and 32-bit)

o Parity chips versus non-parity chips

o ECC vs. non-ECC

o Single-sided vs. double sided

4.3 Identify the most popular types of motherboards, their components, and their architecture (bus structures).

Content may include the following:

• Types of motherboards:

o AT

o ATX

• Components:

o Communication ports

o Serial

o USB

o Parallel

o IEEE 1394/Firewire

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o Infrared

• Memory

o SIMM

o DIMM

o RIMM

o SoDIMM

o MicroDIMM

• Processor sockets

o Slot 1

o Slot 2

o Slot A

o Socket A

o Socket 7

o Socket 8

o Socket 423

o Socket 478

o Socket 370

• External cache memory (Level 2)

• Bus Architecture

• ISA

• PCI

o PCI 32-bit

o PCI 64-bit

• AGP

o 2X

o 4X

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o 8X (Pro)

• USB (Universal Serial Bus)

• AMR (audio modem riser) slots

• CNR (communication network riser) slots

• Basic compatibility guidelines

• IDE (ATA, ATAPI, ULTRA-DMA, EIDE)

• SCSI (Narrow, Wide, Fast, Ultra, HVD, LVD (Low Voltage Differential))

• Chipsets

4.4 Identify the purpose of CMOS (Complementary Metal-Oxide Semiconductor) memory, what it contains, and how and when to change its parameters. Given a scenario involving CMOS, choose the appropriate course of action.

CMOS Settings:

• Default settings

• CPU settings

• Printer parallel port—Uni. bi-directional, disable/enable, ECP, EPP

• COM/serial port—memory address, interrupt request, disable

• Floppy drive—enable/disable drive or boot, speed, density

• Hard drive—size and drive type

• Memory—speed, parity, non-parity

• Boot sequence

• Date/Time

• Passwords

• Plug & Play BIOS

• Disabling on-board devices

• Disabling virus protection

• Power management

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• Infrared

Domain 5: Printers

5.1 Identify printer technologies, interfaces, and options/upgrades.

Technologies include:

• Laser

• Ink Dispersion

• Dot Matrix

• Solid ink

• Thermal

• Dye sublimation

Interfaces include:

• Parallel

• Network

• SCSI

• USB

• Infrared

• Serial

• IEEE 1394/Firewire

• Wireless

Options/Upgrades include:

• Memory

• Hard drives

• NICs

• Trays and feeders

• Finishers (e.g., stapling, etc.)

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• Scanners/fax/copier

5.2 Recognize common printer problems and techniques used to resolve them.

Content may include the following:

• Printer drivers

• Firmware updates

• Paper feed and output

• Calibrations

• Printing test pages

• Errors (printed or displayed)

• Memory

• Configuration

• Network connections

• Connections

• Paper jam

• Print quality

• Safety precautions

• Preventive maintenance

• Consumables

• Environment

Domain 6: Basic Networking

6.1 Identify the common types of network cables, their characteristics, and connectors.

Cable types include:

• Coaxial

o RG6

o RG8

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o RG58

o RG59

• Plenum/PVC

• UTP

o CAT3

o CAT5/e

o CAT6

• STP

• Fiber

o Single-mode

o Multi-mode

• Connector types include:

o BNC

o RJ-45

o AUI

o ST/SC

o IDC/UDC

6.2 Identify basic networking concepts including how a network works.

Concepts include:

• Installing and configuring network cards

• Addressing

• Bandwidth

• Status indicators

• Protocols

o TCP/IP

o IPX/SPX (NWLINK)

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o AppleTalk

o NETBEUI/NETBIOS

• Full-duplex, half-duplex

• Cabling—Twisted Pair, Coaxial, Fiber Optic, RS-232

• Networking models

o Peer-to-peer

o Client/server

• Infrared

• Wireless

6.3 Identify common technologies available for establishing Internet connectivity and their characteristics.

Technologies include:

• LAN

• DSL

• Cable

• ISDN

• Dial-up

• Satellite

• Wireless

Characteristic include:

• Definition

• Speed

• Connections

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A+ Operating System Technologies Exam

For A+ certification, the examinee must pass both this examination and the A+ Core Hardware examination. This examination measures essential operating system competencies for microcomputers hardware service technician with six months of on-the-job experience. The examinee must demonstrate basic knowledge of the Command Line Prompt, Windows 9x and Windows 2000 for installing, configuring, upgrading, troubleshooting, and repairing microcomputer systems.

OS Exam

Domain % Of Examination

1.0 – OS Fundamentals 30%

2.0 – Installation, Configuration and Upgrading 15%

3.0 – Diagnosing and Troubleshooting 40%

4.0 – Networks 15%

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Domain 1: Operating System Fundamentals

1.1 Identify the major desktop components and interfaces, and their functions. Differentiate the characteristics of Windows 9x/Me, Windows NT 4.0 Workstation, Windows 2000 Professional, and Windows XP.

Content may include the following:

• Contrasts between Windows 9x/Me, Windows NT 4.0 Workstation, Windows 2000 Professional, and Windows XP

• Major Operating System components

o Registry

o Virtual Memory

o File System

• Major Operating System Interfaces

o Windows Explorer

o My Computer

o Control Panel

o Computer Management Console

o Accessories/System Tools

o Command line

o Network Neighborhood/My Network Places

o Task Bar/systray

o Start Menu

o Device Manager

1.2 Identify the names, locations, purposes, and contents of major system files.

Content may include the following:

• Windows 9x –specific files

o IO.SYS

o MSDOS.SYS

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o AUTOEXEC.BAT

o COMMAND.COM

o CONFIG.SYS

o HIMEM.SYS

o EMM386.exe

o WIN.COM

o SYSTEM.INI

o WIN.INI

o Registry data files

§ SYSTEM.DAT

§ USER.DAT

• Windows NT-based specific files

o BOOT.INI

o NTLDR

o NTDETECT.COM

o NTBOOTDD.SYS

o NTUSER.DAT

o Registry data files

1.3 Demonstrate the ability to use command-line functions and utilities to manage the operating system, including the proper syntax and switches.

Command line functions and utilities include:

• Command/CMD

• DIR

• ATTRIB

• VER

• MEM

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• SCANDISK

• DEFRAG

• EDIT

• XCOPY

• COPY

• FORMAT

• FDISK

• SETVER

• SCANREG

• MD/CD/RD

• Delete/Rename

• DELTREE

• TYPE

• ECHO

• SET

• PING

1.4 Identify basic concepts and procedures for creating, viewing, and managing disks, directories and files. This includes procedures for changing file attributes and the ramifications of those changes (for example, security issues).

Content may include the following:

• Disks

o Partitions

§ Active Partition

§ Primary Partition

§ Extended Partition

§ Logical partition

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o Files Systems

§ FAT16

§ FAT32

§ NTFS4

§ NTFS5.x

• Directory Structures (root directory, subdirectories, etc)

o Create folders

o Navigate the directory structure

o Maximum depth

• Files

o Creating files

o File naming conventions (Most common extensions, 8.3, maximum length)

o File attributes - Read Only, Hidden, System, and Archive attributes

o File Compression

o File Encryption

o File Permissions

o File types (text vs. binary file)

1.5 Identify the major operating system utilities, their purpose, location, and available switches.

• Disk Management Tools

o DEFRAG.EXE

o FDISK.EXE

o Backup/Restore Utility (MSbackup, NTBackup, etc)

o ScanDisk

o CHKDSK

o Disk Cleanup

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o Format

• System Management Tools

o Device manager

o System Manager

o Computer Manager

o MSCONFIG.EXE

o REGEDIT.EXE (View information/Backup registry)

o REGEDT32.EXE

o SYSEDIT.EXE

o SCANREG

o COMMAND/CMD

o Event Viewer

o Task Manager

• File Management Tools

o ATTRIB.EXE

o EXTRACT.EXE

o Edit.com

o Windows Explorer

Domain 2: Installation, Configuration and Upgrading

2.1 Identify the procedures for installing Windows 9x/Me, Windows NT 4.0 Workstation, Windows 2000 Professional, and Windows XP, and bringing the operating system to a basic operational level.

Content may include the following:

• Verify hardware compatibility and minimum requirements

• Determine OS installation options

o Installation type (typical, custom, other)

o Network configuration

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o File system type

o Dual Boot Support

• Disk preparation order (conceptual disk preparation)

o Start the installation

o Partition

o Format drive

• Run appropriate set up utility

o Setup

o Winnt

• Installation methods

o Bootable CD

o Boot floppy

o Network installation

o Drive Imaging

• Device Driver Configuration

o Load default drivers

o Find updated drivers

• Restore user data files (if applicable)

• Identify common symptoms and problems

2.2 Identify steps to perform an operating system upgrade from Windows 9.x/ME, Windows NT 4.0 Workstation, Windows 2000 Professional, and Windows XP. Given an upgrade scenario, choose the appropriate next steps.

Content may include the following:

• Upgrade paths available

• Determine correct upgrade startup utility (e.g. WINNT32 vs. WINNT)

• Verify hardware compatibility and minimum requirements

• Verify application compatibility

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• Apply OS service packs, patches, and updates

• Install additional Windows components

2.3 Identify the basic system boot sequences and boot methods, including the steps to create an emergency boot disk with utilities installed for Windows 9x/Me, Windows NT 4.0 Workstation, Windows 2000 Professional, and Windows XP.

Content may include the following:

• Boot Sequence

o Files required to boot

o Boot steps (9.x, NT-based)

• Alternative Boot Methods

o Using a Startup disk

o Safe/VGA-only mode

o Last Known Good configuration

o Command Prompt mode

o Booting to a system restore point

o Recovery Console

o Boot.ini switches

o Dual Boot

• Creating Emergency Disks with OS Utilities

• Creating emergency repair disk (ERD)

2.4 Identify procedures for installing/adding a device, including loading, adding, and configuring device drivers, and required software.

Content may include the following:

• Device Driver Installation

o Plug and Play (PNP) and non-PNP devices

o Install and configure device drivers

o Install different device drivers

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o Manually install a device driver

o Search the Internet for updated device drivers

o Using unsigned drivers (driver signing)

• Install Additional Windows components

• Determine if permissions are adequate for performing the task

2.5 Identify procedures necessary to optimize the operating system and major operating system subsystems.

Content may include the following:

• Virtual Memory Management

• Disk Defragmentation

• Files and Buffers

• Caches

• Temporary file management

Domain 3: Diagnosing and Troubleshooting

3.1 Recognize and interpret the meaning of common error codes and startup messages from the boot sequence, and identify steps to correct the problems.

Content may include the following:

• Common Error Messages and Codes

o Boot failure and errors

§ Invalid boot disk

§ Inaccessible boot device

§ Missing NTLDR

§ Bad or missing Command interpreter

o Startup messages

§ Error in CONFIG.SYS line XX

§ Himem.sys not loaded

§ Missing or corrupt Himem.sys

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§ Device/Service has failed to start

o A device referenced in SYSTEM.INI, WIN.INI, Registry is not found

o Event Viewer – Event log is full

o Failure to start GUI

o Windows Protection Error

o User-modified settings cause improper operation at startup

o Registry corruption

• Using the correct Utilities

o Dr. Watson

o Boot Disk

o Event Viewer

3.2 Recognize when to use common diagnostic utilities and tools. Given a diagnostic scenario involving one of these utilities or tools, select the appropriate steps needed to resolve the problem.

Utilities and tools may include the following:

• Startup disks

o Required files for a boot disk

o Boot disk with CD-ROM support

• Startup Modes

o Safe mode

o Safe Mode with command prompt

o Safe mode with networking

o Step-by-Step/Single step mode

o Automatic skip driver (ASD.exe)

• Diagnostic tools, utilities and resources

o User/installation manuals

o Internet/web resources

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o Training materials

o Task Manager

o Dr. Watson

o Boot Disk

o Event Viewer

o Device Manager

o WinMSD

o MSD

o Recovery CD

o CONFIGSAFE

• Eliciting problem symptoms from customers

• Having customer reproduce error as part of the diagnostic process

• Identifying recent changes to the computer environment from the user

3.3 Recognize common operational and usability problems and determine how to resolve them.

Content may include the following:

• Troubleshooting Windows-specific printing problems

o Print spool is stalled

o Incorrect/incompatible driver for print

o Incorrect parameter

• Other Common problems

o General Protection Faults

o Bluescreen error (BSOD)

o Illegal operation

o Invalid working directory

o System lock up

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o Option (Sound card, modem, input device) or will not function

o Application will not start or load

o Cannot log on to network (option – NIC not functioning)

o Applications don’t install

o Network connection

• Viruses and virus types

o What they are

o TSR (Terminate Stay Resident) programs and virus

o Sources (floppy, emails, etc.)

o How to determine presence

Domain 4 Networks

4.1 Identify the networking capabilities of Windows. Given configuration parameters, configure the operating system to connect to a network.

Content may include the following:

• Configure protocols

o TCP/IP

§ Gateway

§ Subnet mask

§ DNS (and domain suffix)

§ WINS

§ Static address assignment

§ Automatic address assignment (APIPA, DHCP)

o IPX/SPX (NWLink)

o Appletalk

o NetBEUI/ NetBIOS

• Configure Client options

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o Microsoft

o Novell

• Verify the configuration

• Understand the use of the following tools

o IPCONFIG.EXE

o WINIPCFG.EXE

o PING

o TRACERT.EXE

o NSLOOKUP.EXE

• Share resources (Understand the capabilities/limitations with each OS version)

• Setting permissions to shared resources

• Network type and network card

4.2 Identify the basic Internet protocols and terminologies. Identify procedures for establishing Internet connectivity. In a given scenario, configure the operating system to connect to and use Internet resources.

Content may include the following:

• Protocols and terminologies

o ISP

o TCP/IP

o E-mail (POP, SMTP, IMAP)

o HTML

o HTTP

o HTTPS

o SSL

o Telnet

o FTP

o DNS

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• Connectivity technologies

o Dial-up networking

o DSL networking

o ISDN networking

o Cable

o Satellite

o Wireless

o LAN

• Installing and Configuring browsers

o Enable/disable script support

o Configure Proxy Settings

o Configure security settings

• Firewall protection under Windows XP

This courseware will prepare you to master the A+ Exams. By completing all of the course work, you will be able to complete the A+ Certification exams with the confidence you need to assure success. More importantly, you will be able to conduct your business with the knowledge that you are among the best and that you really know your stuff.

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Summary

Certification is a long journey. It is important for the student to understand the benefits of completing the journey.

To successfully master the exams, the student must understand the objectives of the exams. Before you take either of the exams, be sure to review the objectives presented here. The exam questions are designed to support each one of these objectives. Just in case there have been any last minute changes, you can go the web site for CompTIA and confirm that you have the latest information. The address for this site is www.comptia.org. Look for certification and the exam blueprints.

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KEYWORDS Exercise

Define each of the following keywords. Hint: There’s a glossary in the back of this book.

Keyword Definition

A+ Certification

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Review Questions - Chapter 1

1. Name three benefits of A+ Certification.

2. Name the two modules required for A+ Certification.

3. What organization is responsible for sponsoring the A+ Certifications program?

4. List all the A+ Exam Objectives that you can remember.

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Chapter 2 – General Knowledge and Terms

Although this course and the A+ exam focus on the modern “electronic” computer, we are going to begin with the basics. This chapter sets the foundation with a summary of the computer and the role of today’s computer professional. You will gain an understanding of the evolution of computers, as it will shed a great deal of light on how they work today. Many of the principles used in the early computers still apply to the modern electronic computer.

The chapter will also concentrate on many of the general terms that you will encounter throughout this course and during your profession as a PC Technician. Let’s begin with how a computer works.

How a Computer Works

A basic understanding of how a computer works is essential to becoming a computer service technician. However, you will also need to define your role as a service technician.

The Role of a Computer Service Professional

In today’s world, the role of the computer professional is constantly changing. Not too many years ago, all you needed to repair a computer was a screwdriver, a pair of needle nose pliers, the documentation for the computer and a good copy of a DOS manual. Although these may still be the basics, you will have to carry an entire library of technical manuals (a laptop with a modem would help) and a box of “special” tools (just to open some computer cases). Today’s computer professional needs to be a technician, a scholar, and a diplomat all rolled into one, as you can see by the following table.

Roles of a Computer Service Professional

Title Skills

Technician Troubleshoot and repair hardware and software efficiently and quickly.

Scholar The wisdom to seek what you don’t know and the perseverance to learn more. Learning never stops.

Diplomat You must instill in the end-user (your customer) the confidence that you are in control and can fix things even though you have “never seen that before!” You must be able to fix the whole problem even if your customer’s (lack of) understanding of the computer is part of the problem.

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Chronology of a Computer

Many of us think only in terms of “electronic” computers. (If you can’t plug it in, is it a computer?) The truth (according to Funk & Wagnall’s Standard College Dictionary) is that to “compute” is to “ascertain (an amount or number) by calculation or reckoning.” In fact, the Chinese about 2500 years ago invented the first computers. They are called abacuses and are still used throughout Asia today.

The Abacus

The abacus is a calculator; its first recorded use was circa 500 B.C. The Chinese used it for addition, subtraction, division, and multiplication. However, the abacus was not unique to the continent of Asia; archeological excavations have revealed an Aztec abacus in use around 900 or 1000 A. D.

The first computer

The Analytical Engine (A Pre-electronic Computer)

The first mechanical computer was the analytical engine, conceived, and partially constructed by Charles Babbage in London between 1822 and 1871. It was designed to receive instructions from punched cards, make calculations with the aid of a memory bank, and print out solutions to math problems. Although Babbage lavished the equivalent of $6,000 of his own money—and $17,000 of the British government’s money—on this extraordinarily advanced machine, the precise work needed to engineer its thousands of moving parts was beyond the technology of the day. It is doubtful whether Babbage’s brilliant concept could have been realized using the available resources of his own century. If it had been, it seems likely that the analytical engine could have performed the same functions as many of the early electronic computers.

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The First Electrically-Driven Computer

Dr. Herman Hollerith of New York patented the first computer, designed expressly for data processing, on January 8, 1889. The prototype model of this electrically operated tabulator was built for the U.S. Census Bureau and computed results in the 1890 Census.

Using punch cards containing information submitted by respondents to the Census questionnaire, the Hollerith machine was able to make instant tabulations from electrical impulses actuated by each hole. It then printed out the processed data on tape. Dr. Hollerith left the Census Bureau in 1896 to establish the Tabulation Machine Co. to manufacture and sell his equipment. The company eventually became IBM, and the 80-column punch card used by the company is still known as the Hollerith card.

Typical 80-character punch card

The Digital Electronic Computer

The first electronic digital computer was built in the basement of a building on the Iowa State campus. This project took place between 1939 and 1942 and was led by John Atanasoff and a graduate student. This machine had many firsts, including binary arithmetic, parallel processing, regenerative memory, separate memory and computer functions, just to mention a few. When completed, it weighed in at 750 pounds and could store 3,000 bits (0.4K) of data. The name given to this computer was ABC (Atanasoff – Berry Computer).

The technology developed for the ABC machine was passed from Atanasoff to John W. Mauchly who is responsible for the first large-scale digital electronic computer. This project, called ENIAC (Electronic Numerical Integrator and Computer) was built at the University of Pennsylvania - Moore School of Electrical Engineering. ENIAC began as a classified military project and was designed to prepare firing and bombing tables for the US Army. When finally assembled in 1945 it consisted of thirty separate units, plus power supply and forced air-cooling. ENIAC weighed in at thirty tons, used 19,000 vacuum tubes, 1,500 relays, and hundreds of thousands of resistors, capacitors and inductors. It required 200 kilowatts of electrical power to operate.

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Although programming of ENIAC was a mammoth task requiring manual switches and cable connections, it became the workhorse for the solution of scientific problems from 1949 to 1952. ENIAC is considered the prototype from which most of today’s computers evolved.

Another early digital electronic computer that played an important part in history was called Colossus I. It was built at a secret government research establishment at Bletchley Park, Hertz, England, under the direction of Professor Max Newman. Colossus I was built for a single purpose: crypto analysis—the cracking of codes. Working from an input of punched paper tape, it was capable of scanning and analyzing 5,000 characters a second. Colossus became operational in December 1943, and proved to be one of the most important technological aids to victory in World War II. It enabled the British to break the otherwise impenetrable German “Enigma” series of enemy codes.

The sixties and seventies were the age of the mainframes. Using the technology of ABC, ENIAC, and Colossus, large computers and emerging companies were the norm for the industry.

As these highlights show, the concept of the computer has indeed been with us for quite a while. The following table provides an overview of the evolution of modern computers—it is a timeline of important events. As you read this timeline for the first time, you will no doubt encounter unfamiliar terminology. For now, don’t worry about it; just experience the history of computers. Also, keep in mind that the timeline you are about to read does not include everything about the history of computers and the computer industry. After completing this course, you should come back and read this timeline again. It will most likely make more sense.

Note: You may not be familiar with some of the terms in this timeline, but all will be explained in the following chapters. The good news is you will not be required to memorize any of this for the A+ test; however, it is an important part of understanding why computers are what they are today.

The Evolution of the Computer:

1971 The 4004—the first 4-bit microprocessor is introduced by Intel. It boasts 2000 transistors with a clock speed of up to 1 MHz (megahertz).

1972 The first 8-bit microprocessor—the 8008—is released. It runs at 200 KHz and can access up to 16 KB of memory.

1974 The 8080 microprocessor is developed. This improved version of the 8008 became the standard from which future processors were designed.

1975 Digital Research introduces CP/M—an operating system for the 8080. The combination of software and hardware becomes the basis for the standard computer. Bill Gates and Paul Allen license their newly written BASIC to MITS. This is the first computer language for a personal computer.

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Bill Gates and Paul Allen found Micro-Soft (hyphen is later dropped). MITS delivers the first generally available Altari 8800. It sold for $375 with 1 KB of memory.

1976 Zilog introduces the Z80—a low-cost microprocessor (equivalent to the 8080). The Apple I comes into existence, although it is not yet very popular. Steve Wozniak and Steve Jobs finish work on a computer circuit board. It is called the Apple I computer. Steve Wozniak and Steve Jobs form the Apple Computer Company (on April Fool’s Day).

1977 The Apple II and the Commodore PET are introduced. These two products use Z80 technology and become the basis for the home computer. Apple’s popularity begins to grow. Bill Gates and Paul Allen sign a partnership agreement to officially create the Microsoft Company. Radio Shack announces the TRS-80 microcomputer.

1978 Intel introduces a 16-bit processor (the 8086 and the math coprocessor 8087). It uses 16-bit registers, a 1-bit data bus, and 29,000 transistors. The price was $350. Intel also introduces the 8088 (similar to the 8086, but it transmits 8 bits at a time). Atari announces the Atari 400 and 800 personal computers.

1979 Apple Computer introduces the Apple II Plus with 48 KB of memory. Motorola introduces the 68000 16-bit microprocessor. It uses 68,000 transistors.

1980 Motorola 68000—a 16-bit processor is important to the development of Apple and Atari. Motorola becomes the processor of choice for Apple. Seagate Technology announces the first Winchester 5.25-inch hard disk drive. It uses four platters, holds 5 MB of data, and costs $600. Radio Shack introduces the TRS-80 Color Computer and the TRS-80 Pocket Computer.

1981 The IBM personal computer is born; it contains a 4.7 MHz 8088 processor with 64 KB (kilobytes) of RAM (Random Access Memory) and MS-DOS 1.0 (three files and some utilities).

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Microsoft begins work on a graphical user interface for MS-DOS. It was called Interface Manager, because it would effectively hide the interface between programs and devices like printers and video cards. This marked the beginning of Windows.

1982 Intel completes development of the 80286 processor—a 16-bit data bus, with 134,000 transistors. It could address 16 MB of memory. You could purchase them for $350 (in quantities of 100 or more).

MS-DOS 1.1 now supports double-sided disks that hold 360 kilobytes of data. Shugart Associates introduces half-sized (1.5 inch high) floppy disk drives. Hercules Computer Technology announces the Hercules Graphics Card, with monochrome graphics at 720x348 resolution.

1983 IBM introduces the XT with a 10MB hard drive. MS-DOS 2.0 arrives—it features a tree-like structure. Apple Computer unveils the Lisa computer. It featured a 5 MHz 68000 processor. Microsoft releases MS-DOS 2.0. Microsoft gives a demonstration of Interface Manager. It consists entirely of overlapping windows appearing to be running programs simultaneously. Microsoft introduces it first “Mouse.” The one millionth Apple II is made. Iomega introduces the Bernouli Box storage device. Novell introduces the NetWare network operating system. Interface Manger officially changes to Windows. It is formally announced and promised for release by April.

1984 The first computer with the 80286 chip—the IBM AT—is sold. It is a 6 MHz machine with a 20MB hard drive and high-density 1.2MB floppy disk drive. Motorola introduces the 68020 processor, a 32-bit version of the 68000. Microsoft releases MS-DOS 3.0 - It includes support for 1.2 MB floppy disk and hard drives up to 10 MB.

1985 MS-DOS 3.2, which supports networks, is released.

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CD-ROM drives are introduced for use on computers. Intel introduces the 16 MHz 80386DX processor with 32-bit registers and a 32-bit (16 MHz) data bus. It has 275,000 transistors and sells for $299. At last, Microsoft ships Windows 1.0 at a cost of $100 per copy.

1986 Not much happened this year. The Intel 80386 market is growing but not many applications can take advantage of its capabilities. Compaq releases a computer with a 386 chip, but software is not yet available to take advantage of the 32-bit instructions.

1987 MS-DOS 3.3 allows operation of 1.44 MB 3.5-inch disk drives and hard drives larger than 32 MB. Apple introduces the Macintosh II and the Macintosh SE. IBM introduces the Personal System/2 (PS/2), Video Graphics Array, and Micro Channel Architecture. A complete departure from previous machines, it does not support the hardware and software available on IBM personal computers or clones. The one-millionth copy of Windows ships.

1988 Microsoft, (with the help of IBM) develops OS/2 (Operating System 2), which allows genuine multitasking and full MS-DOS compatibility. Microsoft also releases MS-DOS 4.0, which boasts a graphical interface. Intel introduces the 80386SX processor. It is similar to the 80386DX but runs on a 16-bit bus. It was a low cost alternative to the 80386DX and was compatible with older hardware. It filled a market niche until software and hardware became available to match 32-bit processing.

1989 Intel introduces the 80486; it contains a 386, a 387 (math coprocessor), and an internal cache controller (offering 2.5 times the performance of a 386 with a coprocessor). Apple introduces the Apple Portable.

1990 Motorola announces the 32-bit 25 MHz 68040 (12 million transistors). Microsoft ships Windows 3.0. Microsoft ships the 50 millionth copy of BASIC.

1991 MS-DOS 5.0 offers a significantly improved DOS shell.

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Intel introduces the 20 MHz i486SX. Just like the 486DX, but no built in math coprocessor.

1992 The Intel i486DX2 processor is introduced, offering 2.5 times the performance of a 486. This marked the beginning of the race for the fastest clock speed. Intel introduces the Peripheral Component Interconnect (PCI) local-bus standard for personal computers.

IBM expands OS/2. Windows enters the scene and grows in popularity. IBM introduces the ThinkPad.

1993 MS-DOS 6.0 is released.

IBM releases OS/2 2.21.

Intel announces the DX4 (tripling the clock speed).

Intel introduces the Pentium processor; it contains over 3 million transistors (a 486 has 1.2 million transistors).

The term “multimedia” (the inclusion of CD-ROMs, sound cards, speakers, and so forth, as more or less standard equipment on new personal computers) appears on the scene. Microsoft launches the Windows NT operating system.

1994 Intel delivers the first 100 MHz processor.

COMPAQ Computer Corporation becomes the largest producer of computers. Dr. Thomas R. Nicely of Lynchburg College notes that the Pentium processor sometimes produces flawed floating-point results, yielding only 4-8 decimals of precision. Digital Equipment Corporation formally introduces it next generation Alpha AXP processor (300 MHz). Iomega introduces the ZIP disk.

1995 Microsoft introduces Windows 95, originally code-named Chicago. It features 32-bit architecture.

IBM has shipped over 1 million OS/2 Warp software packages.

The Internet evolves from its predominate use by government and educational institutions to everyday use by anyone who has a modem.

Computer prices continue to drop!

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IBM purchases LOTUS (maker of the popular spreadsheet 1-2-3).

1995 – 1996 Software manufacturers scramble to make their products compatible with Windows 95.

1996 Intel introduces the 200 MHz Pentium. Microsoft introduces Windows NT 4.0 and the CE operating system for hand-held PCs. CD-ReWritable (CD-RE) is announced.

1997 Microprocessor speeds exceed the 200 MHz mark. Hard drive and memory prices fall while sizes continue to increase.

CD-ROM drives and Internet connections are considered standard equipment for computers.

1998 Processing speeds continue to soar. CPU speeds exceed 450 MHz and Motherboard speeds reach 100 MHz. Multimedia and Internet connections have become the de facto standard for new personal computers. Prices continue to fall towards the $500 mark. USB (Universal Serial Bus) is introduced. Windows 98 becomes the standard operating system for most new personal computers.

1999 Release of Pentium III with processor speeds in excess of 500 MHz. Microsoft introduces Windows 2000 operating system. Multimedia and Internet is considered standard equipment. Cyrix releases the MII Processor. Advanced Micro Devices releases the Athlon processor produce line.

2000 AMD (Athlon) and Intel release the first 1 GHz processors. IBM ships the 10 millionth ThinkPad. Apple introduces the iMac and the G4 Cube.

2001 Intel Pentium 4 is released and reaches speeds up to 1.5 GHz with a 400 MHz system base.

2002 Tablet PCs are introduced into the market place.

2003 Intel P4 is made available at speeds over 3 GHz.

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How Computers Communicate

A modern computer looks like a complicated device. It is made up of many components connected with what seems to be miles of interlocking wires. Despite this seeming complexity, however, just like a calculator, a computer handles information in three stages: input, processing, and output. Each piece of hardware can be classified in one (and sometimes two) of the three stages.

Three stages of computing

Processing

Although processing is the second stage of computing, we’ll start here because these components are the heart of the computer. Computers were initially designed for the business environment; they were intended as tools to do the tedious work of “number crunching” and storing large amounts of often-redundant data. Today they not only fulfill an ever-expanding business role, but also fill our lives with education, entertainment, organization, information processing, and occasionally, frustration. As we enter a new century, they have become a necessity of life and are taken for granted in most households & businesses. Even if you do not own or use a computer, microprocessors run most of our mechanical and electronic devices, including cars.

Input

The ability to process data is an incredible and amazing thing; however, if the data cannot find its way into the processor, nothing will happen. The first stage of computing is input. Input refers to any means that moves data (information) from the outside world into the processor.

Output

All the input and processing in the world won’t do us any good unless we can get the information back (after being processed) so that we may put it to use. The third stage of computing is “output.”

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Input, Output and Processing

Whenever you sit down at a computer and run an application, whether it is a game, a spreadsheet, a database, an accounting program or a word processor, you are an active part of the input, processing and output operation of that computer. Here are some examples.

Examples of Application Types

Application Type Use of Application

Accounting Program Input – data entry, order entry, accounts receivable, etc.

Processing – calculating commissions, payroll, etc.

Output – writing checks, summary reports, invoices, etc.

Word Processor Input – words you type.

Processing – formatting the text (word wrap, fonts, etc.).

Output – storing a file.

Spreadsheet Input – numbers (such as sales figures) you type or provide.

Processing – applying one or more formulas to the data.

Output – showing the results of the calculation in numeric of graphical form.

Database Input – typing information into a database form.

Processing – indexing and storing the database records.

Output – reports showing selected database records.

Game Input – your move.

Processing – the computer figures out how to respond to your move.

Output – the computer’s move.

Language of the Computer

Communication is the act of giving, transmitting, or exchanging information. A key element in developing a device such as a computer is establishing a method of communication, both internally (for the transfer of information between hardware components) and externally (with the outside world). An understanding of this process is fundamental to understanding how computers work.

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Humans primarily communicate through words, both spoken and written. This system works well as long as all participants are in the local area (within hearing or seeing distance). But what happens when we want to communicate over long distances? In ancient times, and up until about a century ago, we would send a messenger with either verbal or written messages. This served its purpose, although it was often slow and sometimes the message (or the messenger) got lost in the translation.

As time and technology progressed, people developed machines to communicate. Before the Industrial Age, items like lanterns were used to send messages over long distances (remember “One if by land two if by sea?”). Early Native Americans used smoke signals—armies of yesteryear used flags and mirrors to send signals from one location to another. Over the years, devices were created to signal or send messages over increasingly greater distances.

The advent of electricity and the telegraph accompanied the Industrial Revolution. The telegraph allowed people to send instant or real-time messages long distances over a single wire—we no longer had to see the person on the other end, or wait for the mail carrier to communicate. All of these methods had one thing in common. They required some method of converting human language to a form of information that a machine or device could transmit. On the receiving end, this data needed to be converted back to a language that people could understand. These early communication devices formed two concepts that are the basis of today’s computers. The first is digital, meaning discrete on or off. The second concept is machine language. Machine language is simply a form of language that a machine can use (usually digital) to process data.

The Telegraph and Morse Code

Telegraphs and early radio communication used a common code for transmissions. Morse code, named after its creator, Samuel F. B. Morse, is based on assigning a series of dots (short pulses) and dashes (long pulses) to represent each letter of the alphabet. These pulses are sent over a wire in a prescribed series. The operator on the receiving end would generally use a “code book” to interpret the code back into letters and words. (Of course, experienced operators became familiar with the code and could interpret each character from memory.)

Today’s computers are similar to the early telegraph—they both transmit information over a wire in a digital fashion using a special code. However, the telegraph’s primary function was to communicate over long distances while the computer communicates internally. Another big difference is that computers use more than one wire and a different type of code (based on multiple wires).

Parallel and Serial Devices

In modern terms, the telegraph could be described as a digital serial communication device. It is digital because it uses some discrete (on/off) signals and serial because it sends each piece of information one bit at a time. If we create a code in which each letter of the alphabet represents some combination of eight pieces of digital information (on or off), and we send each piece of information one at a time, we are communicating with a digital serial device. This form of communication works well (if we have only one wire),

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but it’s slow because we have to send eight pieces of information one after the other to represent one piece of information (a letter of the alphabet). We could save a lot of time if, we could send all eight pieces of information at the same time. The solution is to use eight wires instead of one. By using eight wires, we are sending information in parallel. This is precisely how a computer communicates. The following figure illustrates serial and parallel communication.

Serial and parallel communication

Binary - The Language of Computers (Counting by 2s)

Computers are machines. In order for them to communicate, they need a language of their own. Computer language is called binary; it is based on either being on or off.

Bits A bit is the smallest unit of information that is recognized by a microcomputer. It is similar to a light bulb since it can exist only in two states—it is either on or it is off. A bit is the method used for transmitting information on a single wire telegraph system.

Bytes A byte is a group of eight bits. A byte is required in order to represent one character of information. Pressing one key on a keyboard is equivalent to sending one byte of information to the CPU (the computer’s Central Processing Unit). A byte is the standard unit of measuring memory in a microcomputer—values are expressed in terms of kilobytes (KB) or megabytes (MB). The following table lists units of computer memory and their values:

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Units of Computer Memory

Bit Smallest unit of information; shorthand term for binary digit.

Nibble 4-bits (half of a byte)

Byte 8-bits (one character equals 8-bits)

Word 16-bits on a computer (larger computers can use words that are up to 64-bits long)

Kilobyte (KB) 1024 Bytes

Megabyte (MB) 1,048,576 bytes (approximately one million bytes or 1024 kilobytes)

Gigabyte (GB) 1,073,741, 824 bytes (approximately one billion bytes or 1024 megabytes)

Terabyte (TB) 1,099,511,627,776 bytes (1024 gigabytes)

Exabyte (EB) 1,125,899,906,842,620 (1024 terabytes)

Of course, computers are machines and they do not understand ones and zeros. But they do have the capability of interpreting electrical charges. Like binary numbers, electrical charges can exist only in two states—positive or negative. Computers interpret the presence of a charge as 1 and the absence of a charge as zero. This technology allows a computer to process information.

As previously mentioned, a bit can exist in only two states, on and off. When bits are represented visually:

1 (one) equals on

0 (zero) equals off

The following is one byte of information in which all eight bits are set to zero. In the binary system, this represents a single character—the number 0.

0 0 0 0 0 0 0 0

The binary system is similar to the decimal system, which is used for our everyday numbers and values. With the decimal system, the prefix “dec” stands for ten and means that the numbering system has a base of ten. The binary system has a base of two, since “bi” means two.

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As a PC Technician, you will need to be able to convert the binary numbers that a computer understands into the decimal numbers that we are used to. Fortunately, it’s a lot easier than it looks! First, remember that each digit is either a “1” or “0”, representing “ON” or “OFF”. The computer only understands on or off, so any number or letter could have just as easily represented these numbers.

Starting from the first digit on the right with a value of one (1) the value of each digit is doubled as you proceed from right to left. Remember two is the factor used in the binary system. So the bit on the far right has a value of 1, the next a value of 2, the next a value of 4 and so on through the last bit, which has a value of 128. When the bit has a “1” or “on,” its associated value is added to the value of any other bits with an “on” value. This gives you the value of the byte.

To illustrate, here are some examples of bytes of information:

BYTE—EXAMPLE A

The value of this byte is zero because all bits are off (0 = off).

0 0 0 0 0 0 0 0 8 bits

128 64 32 16 8 4 2 1 # values

BYTE—EXAMPLE B

In this example, two of the bits are turned on (1 = on). The total value of this byte is determined by adding the values associated with the bit positions that are on. This byte represents the number 5 (4 + 1).

0 0 0 0 0 1 0 1 8 bits

128 64 32 16 8 4 2 1 # values

BYTE—EXAMPLE C

In this example, two different bits are turned on to represent the number 9 (8 + 1).

0 0 0 0 1 0 0 1 8 bits

128 64 32 16 8 4 2 1 # values

For those mathematically inclined, you will quickly realize that 255 is the largest number that can be represented by a byte.

Since computers use binary numbers and humans use decimal numbers, it is necessary for an A+ technician to be able to make simple conversions. The following table shows decimal numbers and their binary equivalents (0 to 9). You will need to know this information.

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Decimal Number Binary Equivalent

0 0000

1 0001

2 0010

3 0011

4 0100

5 0101

6 0110

7 0111

8 1000

9 1001

10 1010

11 1011

12 1100

13 1101

14 1110

15 1111

Decimal to Binary Conversion

Note: Notice that in this table, we counted to 15, but have 16 numbers. In computer, the number 0 is a valid number.

Numbers are nice, but it is not practical to represent only numbers with bytes. Remember, people think in terms of words. Since computers need to handle many other types of information, a code is needed to translate between machine language and human language.

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ASCII

As mentioned earlier, the telegraph uses standard Morse code. Remember that this code is transmitted over a single wire using serial communication. Computers use the binary system for communication, based on eight bits or one byte of information being transmitted at one time. To support this, a standard code called ASCII (American Standard Code for Information Interchange) was developed as the basis for computer communication. Basic ASCII consisted of 128 codes that represented the English alphabet, punctuation, and certain control characters. Most systems today recognize 256 codes: the original 128 plus additional 128 codes called the extended character set.

Remembering that a byte represents one character of information, four bytes are required to represent a string of four characters. The following four bytes represent the string 12AB (using ASCII code):

00110001 00110010 01000001 01000010

1 2 A B

The following is the binary representation for the six characters in the word “memory”:

M E M O R Y

01001101 01000101 01001101 01001111 01010010 01011001

Note: It is very important to understand that in computer processing, unlike in typing, the “space” is a significant character. Like any other character, the space has a binary configuration. In computing, the absence or presence of a space is critical and sometimes causes confusion or frustration among new users.

The following table is a complete representation of the ASCII character set. Even in present-day computing, laden with multimedia and sophisticated programming, ASCII retains an honored and important position. Without ASCII, for instance, you could not exchange email with others!

ASCII Character Set

Symbol Binary (1 Byte)

Decimal Symbol Binary (1 Byte)

Decimal

0 00110000 48 V 01010110 86

1 00110001 49 W 01010111 87

2 00110010 50 X 01011000 88

3 00110011 51 Y 01011001 89

4 00110100 52 Z 01011010 90

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Symbol Binary (1 Byte)

Decimal Symbol Binary (1 Byte)

Decimal

5 00110101 53 a 01100001 97

6 00110110 54 b 01100010 98

7 00110111 55 c 01100011 99

8 00111000 56 d 01100100 100

9 00111001 57 e 01100101 101

A 01000001 65 f 01100110 102

B 01000010 66 g 01100111 103

C 01000011 67 h 01101000 104

D 01000100 68 i 01101001 105

E 01000101 69 j 01101010 106

F 01000110 70 k 01101011 107

G 01000111 71 l 01101100 108

H 01001000 72 m 01101101 109

I 01001001 73 n 01101110 110

J 01001010 74 o 01101111 111

K 01001011 75 p 01110000 112

L 01001100 76 q 01110001 113

M 01001101 77 r 01110010 114

N 01001110 78 s 01110011 115

O 01001111 79 t 01110100 116

P 01010000 80 u 01110101 117

Q 01010001 81 v 01110110 118

R 01010010 82 w 01110111 119

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Symbol Binary (1 Byte)

Decimal Symbol Binary (1 Byte)

Decimal

S 01010011 83 x 01111000 120

T 01010100 84 y 01111001 121

U 01010101 85 z 01111010 122

Note: Notice that all letters have a separate ASCII value for upper and lower case. The capital letter “A” is 65 and the lower case “a” is 97.

ASCII Extended Character Set

The ASCII character set uses 7-bits (a string of seven ones and zeros) and thus has values 0-127. With the extended character set, a string of eight ones and zeros is used (8-bit) and so 256 characters are possible.

Counting by 16 – Hexadecimal

Binary works great for machines and computers, but large binary numbers are difficult for programmers to remember. All the ones and zeros work great when machines are conversing, but that language can be somewhat cumbersome for computer designers and programmers. To simplify the representation of numbers and notations, designers and programmers use a numbering system called hexadecimal. Fortunately, as a computer professional, you don’t have to be an expert in hexadecimal, but you do need to know how it relates to numbering and computers.

Where binary is a base 2 numbering system and decimal is a base 10 numbering system, hexadecimal (known affectionately as hex) is a base 16 numbering system. Hex uses the numbers 0 through 9 and the letters A through F to represent the 16 numbers. The numbers 0 through 9 represent their respective values, but the letters A through F are used to represent the values of 10 through 15 (A representing 10, B representing 11, C representing 12, etc.). Why use hexadecimal? The answer is that large binary numbers are difficult for us to remember. For example, if you had to remember 20 binary digits and write them down in the proper order, you will get confused and get some of the 1s or 0s out of order. Breaking the twenty digits into 5 groups of four digits each and representing each group with a single number will make it easier to remember. Since a group of four binary digits can represent a number between 0 and 15, we can replace it with one hexadecimal number. The following table shows the binary, decimal and hex equivalents. We are going to use five binary digits and two hex digits to count from 0 to 21. Just like in the binary to decimal example, there will be 22 numbers but we will only count to 21.

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Binary/Decimal/Hexadecimal

Binary Number

Decimal Number

Hexadecimal Number

00000 0 00

00001 1 01

00010 2 02

00011 3 03

00100 4 04

00101 5 05

00110 6 06

00111 7 07

01000 8 08

01001 9 09

01010 10 0A

01011 11 0B

01100 12 0C

01101 13 0D

01110 14 0E

01111 15 0F

As you can see from the above table, the binary numbers are only four bits long. This is because any value represented by these four bits can be represented in hex. Therefore, the first thing to do to convert a binary number into hex is to break it up into groups of four bits (nibbles). If there are not enough numbers to break evenly into four, zeros are added to the left of the binary number to make it evenly divisible. For example, the eight bit binary number of 01101011 (whose decimal equivalent happens to be 107) would be broken into two nibbles: 0110 and 1011. The hexadecimal value of the first nibble would be 6 and the hexadecimal value of the second nibble would be B. So the cumbersome eight bit binary number of 01101011 could be represented in hex as 6B.

Note: Hexadecimal is case sensitive – the letters A through F must be capitalized!

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Similarly, a 32-bit binary number like: 01000111001010001110101110100110 could be translated into a much less cumbersome hex number as follows:

First, break it into nibbles:

0100 0111 0010 1000 1110 1011 1010 0110

Then assign the corresponding hex value to each nibble:

0100 = 4 0111 = 7 0010 = 2 1000 = 8

1110 = E 1011 = B 1010 = A 0110 = 6

Therefore, the hex representation of the binary number 01000111001010001110101110100110 is 4728EBA6. As you can see, the hex number would be much easier for a human to handle than its binary equivalent.

Memory addresses are represented in hex and this is the reason you need to be familiar with hexadecimal numbers. We will discuss memory addressing later in this text.

Here is a useful trick for learning and converting numbers. If you have Windows, you can use the built-in calculator. It is generally found in: Start>Programs>Accessories>Calculator. After opening it, change it to the scientific view. Notice in the box (upper left below the number field) that there are four radio buttons. [Hex, Dec, Oct and Bin]. Each of these represents a different numbering system. If you type the number 62106 into the calculator and then change the numbering system from Dec to Hex, you will see the Hexadecimal number. Also, if you type a binary number (be sure to select Bin number system first, then change to Dec, you will see the decimal number.

The Microsoft Windows Calculator

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The Computer Bus

Our earlier discussion pointed out the difference between bits & bytes and the difference between serial & parallel data transfers. Within computers and computer equipment, data is moved around on either a single wire (serial) or several parallel wires. These wires or circuit traces (copper lines on a circuit board) are called a bus.

The principle of serial communication—first used by the telegraph—is still employed today for communication over telephone lines. As mentioned earlier in this chapter, communications within a computer need to occur at a much quicker rate; a number of signals are processed at one time. Therefore, the computer moves information through a bus rather than a single wire. There are several types of buses used within a computer and they will be more fully discussed in later chapters. For now, let’s simply look at what a bus is and how it works.

A bus is a group of electrical conductors that run parallel to each other. These conductors can be copper traces on a circuit board or wires in a cable. Normally, they are found in multiples of eight (8, 16, 32, 64, and so on). The early computers used eight conductors for a bus therefore allowing the transmission of eight bits or one byte of information at a time.

Computer bus

The physical configuration of a bus, whether it is a circuit board, or a traditional or flat cable, is not as important as its function. The purpose of a bus is to provide a common path to transmit information (in the form of code) to all parts of the computer. Therefore, any device that is connected to the bus can receive or send information to any other part of the computer that is also connected to the bus. This is not unlike the aforementioned telegraph. A single wire was strung from one end of the country to the other, and any town that tapped into the wire could exchange information with any other town also connected to the wire.

A familiar example of a bus system is the electrical wiring in a home or office. The 120-volt AC outlets are wired (with three wires—hot, neutral, and ground) in parallel from one outlet to another. Each time a device is plugged in, it is connected to the bus (in parallel).

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Connecting to a bus

Remember: in a computer, a bus is a set of parallel wires or lines to which the CPU, the memory, and all input/output devices are connected. Everything in a computer is connected to a bus. The actual number of wires or lines in a bus may vary from one computer to another. The bus contains one line for each bit needed to give the address of a device or a location in memory. It also contains one line for each bit of actual data being transmitted from device to device. A manufacturer may use additional lines for power or other communication within the computer. When we are speaking of buses within a computer (data bus, expansion bus, or address bus) we are speaking of a specific number of wires dedicated for a specific purpose.

Components of a Computer

As you might expect, the components of a computer reflect the function of the machine, specifically, the three stages of computing, as outlined earlier in this section. Considering these three stages, lets take a closer look at some of the components that make up a computer and classify them by their stage.

Processing

The CPU (Central Processing Unit) is considered the brain of any computer. This one component or “chip” does all the number crunching and data management. It is so important that whole generations of computer technology are based and measured on each “new and improved” version of the CPU.

The CPU generally refers to the processor. But the CPU actually encompasses several other components that support it with the management of data. These components, when working in harmony, make up the computer we know today. Let’s look at some processing components.

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Motherboard – large circuit board, contains other components

Chip set – group of computer chips that manage and control the computer system

Data bus – group of parallel conductors found on motherboard, used by CPU to send and receive data from all devices

Address bus – group of parallel conductors used to address memory locations, determines what information is sent to, or received from the data bus

Bus

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Expansion slots – sockets that allow additional devices to attach to the motherboard

Clock – establishes maximum speed at which the processor can execute commands

Battery – prevents unique information about the setup of the computer from being lost when power is off

Memory – stores temporary information that CPU and software need to keep running

Input

An input device is any device that provides a path for information to flow from us into the computer. Let’s look at some of the input devices you will encounter as a technician.

Keyboard – primary input device

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Mouse – used with graphical user interface environments to point and select objects

Scanner – converts printed or photographic information to digital form

Microphone – allows input of voice or music to be converted to digital form

CD-ROM – Compact Disc-Read Only Memory, stores large amounts of data

Firmware – computer chip that contains preprogrammed information, permanent

memory

Software – program in digital format that can be input into CPU to run applications

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Output

Now, let’s take a look at some output devices.

Printer – generates “hard copy”

Display – monitor, primary output device, visually displays text and graphics

Plotter – uses pens to draw an image

Speakers – reproduce sound

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Input/Output (I/O)

Many devices can handle both input and output functions. These devices are called I/O devices, a term you will encounter quite often.

Floppy drive – reads and writes to low-capacity, removable magnetic disk

Hard drive – high capacity internal magnetic disks for data storage

Modem – converts computer data to information that can be transmitted via telephone

wires

Network card – allows several computers to connect to each other

WORM drive – version of CD that allows Write Once Read Many

Tape drive – large capacity storage, ideal for backup, saves in linear format

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Support Hardware

We have been looking at various devices that are required to provide the data processing within our computers. Additional pieces of hardware can be used to support safe operation of a computer. Let’s look at a few of the devices that protect and enhance the value of a computer.

Power supply – converts local power source to 5 and 12 volts DC

Switch box – allows user to manually switch cable connections

Surge suppressor – prevents large power spikes from damaging computer

UPS – uninterruptible power supply, acts as surge suppressor and power leveler

Cabling and Connectors

Cables and connectors are a very important part of the computer. They are also a very important part of the life of a computer technician. By understanding the various types of cables and connectors, a computer technician can often identify components and their functions. While cables and connectors look alike, they are not always the same and one that is incorrectly installed will cause failures.

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Parallel Printer Cables

Parallel printer ports and cables are used to connect printers and other add-on items such as CD-ROMs, tape drives, and scanners. Centronics Corporation invented the most common type. This is an 8-bit parallel connection. It uses eight wires for data transmission and additional wires for sending control signals between the printer and the computer. These control signals tell the computer when to stop or start sending data. A “standard” printer cable is configured with a 36-pin Centronics connector on the printer end of the cable and a standard 25-pin DB (Male) on the computer end of the cable. A standard 25-pin DB (Female) connector found on the back of the computer designates it as a parallel Port.

Standard 25-pin DB Connector

With the early dot-matrix printers, communication between the computer and printer was one-way or uni-directional. The data was sent as plain ASCII code, in a continuous stream of data one byte at a time. As printers and operating systems evolved, a more sophisticated method was required. The printer needed to communicate back to the computer to tell it when it was ready to receive data. These printers required bi-directional communication. An organization called IEEE (Institute of Electrical and Electronics Engineers (pronounced: I triple E) formed a group to oversee the creation of standards for printer ports. The results of their work (known as IEEE 1284 Printer Modes) is as follows:

Bi-Tronics A modified Centronics connection by Hewlett-Packard. It utilizes bi-directional communication allowing the printer to send messages to the computer (out of paper, paper jam, etc.). This standard is considered the original bi-directional printer mode and can transfer data at 80-300Kb/sec.

EPP Enhanced Parallel Port - features 2MB/sec data transfer rates, bi-directional 8-bit operation, addressing to support multiple (daisy-chained) peripherals on a single computer. These ports are used with scanners and high-speed printers.

ECP The Extended Capabilities Port was developed by HP and Microsoft. It features 2 MB/sec data transfer and bi-directional 8-bit operation. These ports can designate whether or not the data being sent to the printer are commands or the data to be printed. ECP supports CD-ROM and scanner connections, RLE data compression, and DMA support to increase transfer speed and reduce processor overhead. It is faster than EPP.

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Communication Cables

A serial port allows a computer to send data long distances by converting parallel data to serial data. Typical computers will have one or two serial ports usually designated as COM1 and COM2. The “standard” port is a 9-pin male connector on the computer (25-pin cables are also available).

Standard 9-pin DB Connector

IEEE 1394 High Performance Serial Bus

The newest, (and maybe we should say “hottest”) connecting device today is the IEEE 1394 High Performance Serial Bus. This innovative connection method is expected to replace and consolidate the serial and parallel connectors that are used today. In addition, it will replace Centronics parallel, RS-232C and even SCSI. It provides for very high data transfer speeds of 400 Mbps today, and much higher rates to come.

This implementation provides the following improvements:

• A common plug-in serial connector for connecting the computer to many different types of peripherals.

• A thinner cable than is used for parallel cables.

• High-speed data transfer rates, with rates expected to climb even higher in the future.

• Hot-plug and plug compatible. This means that you can attach a new device and it will be detected without the bother of rebooting the computer.

• Up to 16 devices can be chained together in several different ways and require no terminators or complicated set up issues.

• Peer-to-peer interface – this means that a device (such as a camcorder) can work with another device without being plugged into a computer.

There are two levels of IEEE 1394: One is used for the bus within the computer and the other for the interface between the device and the computer. A bridge is used to connect the two environments. This device functions as if a peripheral device were attached in slots located inside the computer and sharing a common memory space, thus allowing for the much faster data transfer rates.

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There are two types of data transfer associated with IEEE 1394: Asynchronous and Isochronous. The traditional asynchronous is for load and store applications where the application is interrupted as a given amount of data arrives in a buffer. Isochronous on the other hand ensures that data flows at a pre-set rate so that the application can handle it in a more timed way. This is extremely helpful in multimedia environments, as it reduces the need for buffering and allows for a more smooth and continuous presentation for the viewer.

The 1394 standard requires that a device be within 4.5 meters of the bus socket and assuming that 16 devices are chained together, this means that the last device may be as much as 72 meters away from the computer before attenuation begins to occur.

FireWire™ is Apple Computer’s version of this new IEEE standard. It allows up to 63 devices to be chained together and has data transfer speeds of up to 400 Mbps.

IEEE 1394 BUS/CONNECTOR

Cable Pin Assignments

As a computer technician, you will encounter many cables. Often, they will look the same, but will not function the same. The main difference between cables is that although they use the same connectors, the connection of the wires to the pins on the connectors is different. If the wires are not connected to the correct pin on each end of the cable, it will not function properly. For example, if you purchase a cable with 25-pin connectors on both ends, it could be used for either serial communication (a modem) or parallel communication (a printer). How do you know the difference? Unless it is clearly labeled on the cable itself, you will not know without trial and error. Typically, parallel cables are labeled “data” and communication cables are labeled “communication” or “serial.”

A good example of a cable with wire switches is the null modem cable. Null modem cables are used to connect two computers together without using a modem. The transmit and receive wires in the cable are switched to make the computers “think” they are using modems. You can also purchase a null-modem connector to fit to one end of a serial cable. This will allow direct connection of two computers using a standard cable.

Other Cables Types

There are many different types of cabling both inside and outside of a computer. We have so far discussed the two most common (parallel and serial). The following describes other types of cables that you will find in a computer.

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Data Cables

Data or flat ribbon cables are usually found inside the computer and carry data signals between the motherboard and the hard drive or CD. They can also connect an external parallel or serial port connector to the motherboard. They are provided in various sizes based on the number of wires. The important thing to remember when using these cables is to match the number of wires (and connectors) to the device. In addition, you will need to be able to identify the number one wire on the cable. It is on one side and is red. Matching the number one wire to the correct pin when installing will insure the correct connection.

SCSI Cables

SCSI (Small Computer System Interface) cables come in a variety of sizes depending on the type of SCSI used and the manufacturer of the device. SCSI devices will be covered in more detail in the chapter on storage. Typically, internal cables are flat ribbon type and external cables are shielded bundles.

All cables and connectors should be inventoried before starting a SCSI installation.

Keyboard Cables

Keyboard cables are supplied with different connectors. Earlier versions used either a serial connector (these should never be plugged in with the power on) or a 5-pin DIN connector used with AT and ATX motherboards. Most new keyboards use a 6-pin DIN connector (the same as used on a PS/2 mouse). Connectors are available to convert the 5-pin DIN to a 6-pin DIN mini. Although they have a different number of pins, they use the same wires and pin-outs. Data is sent serially to the keyboard via the keyboard interface. Data is written to the controller’s Input Buffer to accomplish this. Keyboard data passes through pin 2 of the connector, while clocking signals move through pin 1. A keyboard reset, which can be connected to the systems’ reset line, is included at pin 3. Ground and +5VDC connections are applied to the keyboard through pins 4 and 5.

Troubleshooting Cables

Cables and connectors are a very common cause of problems associated with computers. Here are a few suggestions to use when troubleshooting:

• If a peripheral device doesn’t work, always check the cables, especially if “it worked OK yesterday.” The simple act of moving a printer from a desk to a shelf can cause an improperly secured cable to come loose.

• Check for bent or broken pins on the connector. Sometimes, bent pins can be repaired, however, they will always be susceptible to damage later as the pin has been weakened.

• If a connector/cable doesn’t fit or you have to push hard to make the connection, something is wrong. Either a connector is damaged or they are not the right matches.

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• Check for worn or frayed cables. A physically damaged cable can have broken or shorted wires.

• Make sure you have the right cable. Some cables such as a null modem cable will look just like a standard communications cable, but will not work with a modem.

Identifying Cables and Connectors

There are many different cables and connectors found throughout a computer. Often they look similar, but are not the same. One of the jobs of a computer technician is to identify these cables and connectors. The following table describes common cables and their connectors.

Cables and Connectors

Function Computer Connector Cable Connector

Communication (serial)

9-pin or 25-pin male 9-pin or 25-pin female

Printer (parallel)

25-pin female 25-pin male

Monitor (VGA and SVGA) often, the connectors are blue

15-pin female (three rows of pins)

15-pin male (three rows of pins)

Monitor (MGA and CGA)

9-pin female 9-pin male

Game port (joystick)

15-pin female (two rows of pins)

15-pin male (two rows of pins)

Keyboard

5-pin DIN female or 6-pin DIN female (PS/2)

5-pin DIN male or 6-pin DIN male (PS/2)

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Summary of Connectors

Computers use a variety of connectors. Here is a summary of the most common connectors and their uses. This list includes common cables and those used for communication (modems and networks).

Common Connectors

Type Used With

DB-9

Serial Ports – External Modem, Mouse, Printer, Digital Camera

DB-15

Monitors and game ports, network connections on network cards (Joysticks)

DB-25

Parallel Port – Printer, Scanner, Removable Drive

RJ-11

Standard Telephone Connector – 2 wires

RJ-12

Standard Telephone Connector – 4 wires

RJ-45

Network connector – twisted pair

IEEE 1394

Fire Wire – high speed port (digital cameras/camcorders)

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Type Used With

BNC Connector

Network connector - coaxial

PS2/Mini-DIN

Mouse, Scanners

Centronics

Printers

USB

Universal Serial Bus, allows multiple peripherals, provides “hot-plug,” data transfer limited to 12 Mbps (used for a mouse, scanner, newer printers, digital camera, etc.)

SC

This connector is used with fiber optic cabling.

ST

This fiber optic cabling connector is sometimes referred to as a “twist-on” connector.

IDC/UDC

IBM-type Data Connector or Universal Data Connector, originally used with STP cabling in a Token Ring network. It is both male and female and they plug into one another by flipping one of them upside down.

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Summary

This chapter covers a lot of basic information. At this point in your studies, we have defined many general aspects of computers and computing. As you move on into future chapters, you may want to review some of these terms. You will be seeing them often in the remainder of this study guide. The following summarizes the key points of this chapter:

• The computer technician of today must wear a few different hats.

• There is more to repairing a computer than just knowing how to make it work.

• Computers have been around a long time. The ancient Chinese first developed computers (the abacus).

• Modern computers have followed the growth and technology of the electronics industry.

• The role of the computer technician has paralleled the evolution of the computer. A computer technician must also be a scholar and a diplomat.

• The development of rudimentary electrically powered computers began in the 1950s and 1960s.

• The electronic digital computer, as we know it today, began development in the 1970s.

• The “standard” personal computer has gone through several stages of evolution characterized by improvements to the processor, internal architecture, and types of storage devices.

• All computer hardware can be classified by its primary function (input, output, or processing).

• Any time you sit down to a computer and run an application, you are part of the input, processing and output cycle.

• Binary is the language of computers.

• Engineers use hexadecimal as shorthand for binary. Hexadecimal is based on the number 16.

• A bit is the smallest unit of information that is recognized by a microcomputer.

• ASCII is the basic code for computers.

• A bus is the physical method of moving data inside a computer.

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• A bus may take on many different shapes (wires, ribbon cables, circuit traces), but it is a group of parallel wires.

• An A+ technician must be able to convert decimal numbers to binary and binary numbers to decimal numbers.

• A computer uses a bus to move data from one device to another.

• Cables and connectors are an important part of computer. As a technician, you will have to be able to identify various cables, their connectors, and how they are used.

• The latest innovations in connectors are the implementations of the IEEE 1394 standard.

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KEYWORDS Exercise

Keyword Definition

Address bus

Battery

Bit

Bi-Tronics

Byte

CD-ROM

Chip set

Clock

CPU

Data bus

Display

ECP

EPP

EB

Expansion slots

FireWire

Firmware

Floppy Drive

GB

Hard Drive

Keyboard

KB

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Keyword Definition

MB

Memory

Microphone

Modem

Motherboard

Mouse

Network card

Nibble

Plotter

Power supply

Printer

Scanner

Software

Speakers

Surge suppressor

Switch box

Tape drive

TB

UPS

Word

WORM drive

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Review Questions

1. What is an example of an early electronic computer?

2. What are the three roles of today’s computer service professional?

3. What is the definition of a bus in a computer?

4. What is the meaning of digital?

5. What is the difference between serial and parallel communication?

6. What is binary code language?

7. How does ASCII use binary code to represent numbers or characters?

8. Define a bit.

9. Define a byte.

10. What decimal number is represented by the following binary number: 00001001?

11. A computer doesn’t really understand ones and zeros. What do ones and zeros really represent to a computer?

12. Computer buses are normally found in multiples of _________ wires or traces.

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13. What is the standard for Printer Modes?

14. You need to connect a printer to your computer and found a cable with two DB-25 pin female connectors. Can you use this connector?

15. Name the connection types that allow for “hot plugging.”

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Chapter 3- Basic Electricity and Safety

There is no way around it, if you are going to be a computer technician, you will have to know something about basic electricity. You need to be able to test electrical outlets and computer components, and most importantly, do so safely.

Electricity Review

Electricity is what makes a computer run. Without it, a computer might as well be a doorstop. This may seem like a very fundamental statement, but it is true. This chapter begins with the study of electricity - the power that drives a computer. Since all components of a computer need power to run (whether plugged into a wall outlet or a battery), a computer professional must first understand the principles that govern electricity before understanding some of the problems encountered when hardware fails.

The energy or power to drive a computer is derived from electricity. Whether it uses 120 Volts AC (US standard), 220 Volts AC (European Standard) or a battery, without some source of this power, a computer is useless. Computers require a reliable source of power. As computer technicians, we do not have to be electricians or electronic experts. We do however need to be able to perform some basic tests to determine the reliability of the power provided to our computer and its components.

The best way to get started with an understanding of electricity is with a few definitions.

Electricity: A fundamental property of matter, associated with atomic particles whose movements, free or controlled, lead to the development of fields of force and the generation of kinetic or potential energy.

Volts: The unit of electromotive force, or the potential energy that, when steadily applied against a resistance of one ohm, will produce a current of one ampere. Voltage is also considered the potential energy of a circuit.

Ampere: A measurement of current strength. High amperes can mean certain injury or death.

Ohm: A unit of electrical resistance to the flow of DC current.

Impedance: Resistance to the flow of AC current – measured in ohms.

Power: Strength or force actually put forth. Electrical power is measured in Watts which equals Voltage x Current.

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All Computer Professionals should know one formula. From this formula, or a derivation of this formula, all basic power calculations can be performed. The name of this formula is “Ohm’s Law.”

Ohm’s law states that the current flowing through a conductor, or resistance, is linearly proportional to the applied potential difference (volts). In mathematical terms, this means:

IRV formulas

Resistance

Current

Volts

R= Resistance in Ohms (Ω), V = Voltage and I = Current in Amperes

By memorizing any one of these formulas, the other two can be easily derived using simple algebra. For example, the voltage (potential energy of the circuit) equals the amperage (the current or flow of electricity) times any resistance to that flow of electricity. From this, it can be seen that for a given voltage, the more resistance in a circuit, the lower the current flow.

Direct Current (DC)

The first sources of electricity were based on the concept of DC or direct current. When Ben Franklin was flying his kite, he was seeking DC electricity. DC is the same kind of power that we get from batteries. With DC, the current or electrons move in one direction. If you notice, a battery has distinct poles, one positive, and one negative. The current flows from the negative pole to the positive pole. The advantage of using DC power is that it is easy to control. DC is the power of choice for electronic equipment. Computers use low voltage DC power to operate their components.

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DC Power

DC Voltage

Alternating Current (AC)

AC or alternating current is the type of power that we get from the electrical outlets in our houses. The term AC power means that the flow of electrons in the wires moves back and forth or alternates. There are no positive or negative poles. The reason that we use AC power in our businesses and homes is that it is a very efficient way to transport power over long distances. AC power is measured in terms of voltage and frequency. Voltage represents the potential power and the frequency represents how many times per second the voltage alternates. Typical power is delivered to our homes as 110 to 120 Volts at 60 Hz (Hertz – cycles per second). In many nations (Europe for example), standard power is 220 Volts at 50Hz).

Flow of Electrons

The Power Company delivers electricity to our house (or business) with three wires. Two of the wires are called “hot” and one is a neutral (the bare wire that runs from the breaker box to the power pole). The measured voltage between the two “hot” wires is 220 to 240 VACS, while the measured voltage between either of the hot wires and the neutral wire is 110 to 120 VACS. These voltages are called nominal voltages as they can vary by ± 3%.

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AC Volts

AC power is supplied to a computer via the electrical outlets or receptacles and then converted into DC power to run the components inside the computer. When connecting a computer or any other electronic equipment, you must be sure to use a properly grounded outlet. These outlets will have three slots and will require a three-prong plug. Most modern construction today will require all outlets to be of this type, however, there are still some older buildings and houses that do not meet these new codes. While you can still purchase an adapter to convert the three-prong plug that comes with a computer to a two-prong plug for these older receptacles, it is not advised and is dangerous. The reason for the third connection (the small round one) is to provide a safety ground. This will protect you and you’re computer from short circuits. The grounded receptacle provides a direct connection to ground giving the electricity an alternate path should things get out of control. The following figure shows the proper outlet to use.

The Right Outlet

Measuring Electricity

A computer technician does not need to be an electronic technician to be successful. Electronic technicians learn how to test electronic equipment on a component level. As a computer technician, you will not need to test at this level, as you will be more concerned about whether or not the device works or not. Testing at the device level does not require the sophisticated equipment as testing at the component level, however, few electronic testing techniques will be helpful for the computer technician. The most important tool that you as a computer technician can use for device testing is the multimeter. Other names for this device are a VOM - Volt Ohm Meter or a DVOM -Digital Volt Ohm Meter. Beyond randomly replacing parts until finding the bad one, the electrical test

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meter is probably the best (and most practical) tool for troubleshooting electrical problems. In this section, we are going to look at the multimeter and how to use it to do some basic component testing.

The Multimeter

The name multimeter was derived from its ability to measure several different parameters. You can test for AC and DC voltage, resistance, and continuity. Some meters will let you test for current as well, but only low amounts (less than 10 amps). With it, you can test various electronic components as well as the electrical power in the computer. Most will consist of a digital or analog meter or display, a pair of wires with probes (one black and one red) and a switch for adjusting the range of settings to be measured. The red wire is considered the positive probe and the black wire is considered the negative or ground probe.

Multimeter

Testing AC Power

Any time that you install a computer in a new location, you should confirm the power source at the outlet. This is especially true for new construction. In the event an error was made that causes the voltage to be outside of the specifications (either two high or too low), problems are sure to arise.

Note: I have tested a standard outlet in an older building that was recently renovated and found it to be 220 VAC not 120 VAC. Good thing I didn’t plug my computer in first!

Testing AC Outlets with a Multimeter

Before testing an outlet, you will need to be sure that the meter is properly setup. Some of the newer and more expensive meters will have automatic settings for voltage range and will make adjustments accordingly. However, you may still have to tell it whether

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you are measuring AC or DC voltage. If the black and red wires are not permanently wired to the meter, make sure that the black wire is connected to the common (-) hole and the red wire is connected to the Volts (+) hole. Be careful; if this lead is placed in the wrong hole (Ohm or Amp), it can cause permanent damage. This should be the first thing you check when power is gone.

Make sure that your multimeter is set for AC voltage and that the range setting is at least one setting higher than what you anticipate the voltage to be. A setting of 200 volts or higher will work. With the meter properly configured, conduct these three tests.

Multimeter Tests

Hot to Neutral This test will make sure that the correct voltage is present. Place one lead in each of the two vertical slots. The reading should be 110-l20v AC.

Hot to Ground This test will make sure that the receptacle is correctly wired. Place one lead in the smaller of the two vertical slots and the other in ground. The reading should be the same as the first test.

Neutral to Ground

This test will determine that the receptacle is safe. Place one lead in large slot and the other in ground or round hole. The reading should be 0 volts.

If you are looking for a quick and dirty way to test electrical outlets, you can go to your local hardware or home improvement store. They will offer a variety of simple outlet testers. With these devices, you just plug them into an electrical outlet. Most of them will test for all three components. If the power is OK, you will see a green light indication that all is well. These devices while not very accurate, will give you a good pass/fail indication of the power source. On any new installation, especially in a new building, you should always check the power source at the outlets before plugging in a computer or electronic equipment.

Testing for AC in DC

Sounds odd, testing for AC in DC. But, in a computer, the AC voltage from the electrical outlet is converted to DC for use by the components in the computer. Sometimes the conversion and filtration is not working properly and some AC voltage is superimposed on the DC voltage. If the AC component, also called ripple or noise is excessive, it can cause problems. You can test for AC ripple with your multimeter and a small .1 ufd capacitor (micro-farad). To test for ripple, connect the capacitor in series with the red probe on the multimeter. Then set the selector switch on the multimeter to AC and test the DC voltages. The capacitor will remove the DC component and you will be able to read the amount of AC or ripple.

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Testing Resistance

Resistance is the measurement of opposition to the flow of current. Resistance is measured in terms of Ohms (hence Ohm’s Law). In electronic documentation and sometimes on the device itself, the resistance value will be listed as a number followed by the ohm (Ω) symbol. Resistance is measured by placing one lead of the meter on each side of the circuit or component to be measured. Taking resistance measurements for a component, while it is still soldered in its circuit, can lead to an inaccurate reading, as any other component connected to the circuit can effect the total resistance measured. Unlike voltage checks, resistance checks are made with the power OFF. Connecting a meter setup to read resistance to an electrical outlet will damage the meter and possibly you.

Be careful when measuring resistance. If the meter is set too high or the resistance of the resistor is too high for the meter, you will get an inaccurate reading.

Testing continuity

The purpose of continuity testing is to confirm a complete electrical circuit. For example, check to see that a wire is not broken. Most multimeters have a “continuity” setting, which will indicate a complete circuit by either a light or by generating a sound. When you connect both leads of the meter to each end of the device you are testing, a positive test (the light comes on or it makes a noise) means that the circuit is complete. If the test is negative (no light or noise), the circuit is broken. If your meter does not have a continuity setting, it is still possible to test for continuity. All you need to do is use the resistance setting and test the device. In a wire for example, the resistance reading for continuity would be zero – meaning that current is flowing without resistance. If the wire is broken, the resistance reading will be infinity or maximum – meaning that no current is flowing.

Testing a Power Supply

A computer power supply is the front end of a computer. Without the proper voltages both coming into the power supply and from the power supply to the motherboard, a computer will not function properly. While power supplies rarely fail, they can be the source of some problems. Power supply failures generally manifest themselves either as a total failure or as intermittent failures.

Total failures are easy to diagnose – nothing happens. Anytime you suspect a total failure, you should always check the power source at the outlet first, then make sure that your power strip is plugged in and turned on. Finally, make sure that the computer is plugged in. Don’t assume anything.

Power supplies are self-contained units and are not normally repaired by computer technicians. Actually, they are low-cost items and it will most likely be more economical to replace, rather than spend the time repairing. Servicing the inside of a power supply is outside the scope of the A+ certification, however, you will need to know how to determine whether or not a power supply is good or bad. Testing a power supply is

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simple and the only tool you need is a multimeter. There are only four steps to testing power supplies.

The first step is as mentioned above, make sure that there is power to the power supply. Step two is to make sure that the on/off switch is working. On/off switches vary so you may have to check the documentation that comes with the computer. Normally, the power supply and on/off switch is considered part of the chassis or case. Be careful when checking the switch, they usually carry 120 Volts from the source power. Some of them have wires that run from the power supply to the front of the case and others will have a mechanical connection from the front to the power supply. Step three is to make sure that any fuse is OK. If the fuse is bad, you will need to be careful and replace it with an identical one. A bad fuse is often the symptom of another problem rather than the problem itself. If you replace the fuse and it burns out again, you most likely have a more serious problem.

The first three steps are the easy ones and are confirming that power (AC) is being supplied to the power supply. The last step involves testing the output (DC). To complete the final test, you will have to remove the case cover and locate the power connectors to the motherboard. These are called the P8 and P9 connectors. We will discuss more details of these connectors elsewhere in the course.

To test the output, you will need to set your multimeter at around 20 volts DC since you will be testing 5 and 12-volt connections. With the power ON, touch the black (negative) probe to the black wires on one of the connectors and the red probe to the red or yellow wires. Make sure that you are contacting the metallic part of the wire and not the insulation. Black to red should read about 5 volts and black to yellow about 12 volts. On an AT or XT power supply, the P8 connector provides the 12 volt power and the P9 connector provides the 5 volt power. If the power supply is good, the reading at the P8 connector wires should be between 11 and 13 volts. Any reading less than 10 and the power supply should be replaced. But before replacing, you will need to make sure that the problem is in the power supply and not something else in the computer. To continue checking, you will need to remove each of the connectors (P8 & P9 and the ones connected to the drives) one at a time and test for changes. If after removing a connector, the power returns to normal, you have isolated the problem to whichever device when unplugged caused the power to return.

Electronic Components

As a computer technician, you should be familiar with the more common types of electronic components and how to test them. The following is a description of basic electronic components and how to test them.

Capacitors

Capacitors are used to smooth or remove ripple from DC voltage. They act like a small rechargeable battery. When power is applied, the capacitor will charge to its full capacity. When the power drops, the capacitor will begin to discharge thus smoothing the voltage.

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Capacitors

The size of a capacitor is measured in terms of farads. Since most capacitors used in electronic equipment are small, the common unit of measure is the microfarad (uf). You will find many small capacitors on circuit boards. Most of them will look like a small disk with two wires. These devices use small amounts of current and rarely fail. If they fail it is normally caused by a massive power surge in which case there will be more damage than just the capacitor. If you notice discoloration or burned spots, the capacitor may be bad. To test these, you will need to remove them from the circuit board and use a special tool (a capacitor tester). Since this is beyond the scope of normal computer repair and failure of this magnitude will probably require replacement of the device, you will only need to be able to recognize them.

There is another capacitor found in electronic equipment that is prone to failure. These are called electrolytic capacitors. They look like a small can and have two wires on one end. Electrolytic capacitors are different from other capacitors in that they are sensitive to the polarity of the circuit. One wire is labeled as positive (+). The other wire, while not normally labeled, is negative (-). They must be installed correctly or they will not work properly and may be damaged. Electrolytic capacitors typically hold a large charge for a long time. The larger the capacitor, the greater the charge is, and the more dangerous to work with.

To test an electrolytic capacitor all you need is a multimeter. First, make sure the power is turned off. Then set the selector to resistance - ohms. Place the black lead of the multimeter on the negative capacitor lead and the red lead of the multimeter on the positive lead. Generally, capacitors will fail by shorting. Therefore a continuity test will indicate 0 resistance if the capacitor is bad. If your test indicates a high resistance, the capacitor is most likely okay.

Note: When testing a large electrolytic capacitor, the indicator will show an increasing reading until the capacitor is charged. It will stabilize when the capacitor is fully charged. To test again, you will have to discharge the capacitor by shorting the two leads together. It is also a good idea to discharge a capacitor before testing. Simply short out the leads.

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Coils

A coil is also called an inductor. It provides resistance to AC current and no resistance to DC current. Coils are simply wire wrapped in loops. Sometimes the wire is wrapped around a piece of ferrous metal. Coils are used in conjunction with capacitors to provide filtration when converting AC to DC. Failure of a coil is usually indicated by discoloration or burning of the wires. Testing a coil is simple. Since a coil is made of wire, testing is similar to a transformer:

Inspect the coil for visual signs of deterioration.

Turn the power off and do a conductivity test: Set the meter the same as for a capacitance or resistance check. You will need to disconnect one end of the coil before starting the test. Put the leads across the coil and note the reading. Any reading greater than zero indicates that the coil is not open. This test is only an indication of whether or not a coil is bad. To do a complete test will require removing the coil from the part and using an inductor tester. This is a special tool designed specifically for this job.

Coil

Diodes

A diode is a device that will let current flow in only one direction (from the cathode to the anode). Two or more diodes connected to an AC supply will convert the AC voltage to DC voltage. These diodes together (whether a single component or several individual components) are called a rectifier.

Diodes

Fuse

Fuses come in a variety of sizes and shapes. You are probably most familiar with the glass tube variety. The wire inside determines the capacity of the fuse. As the flow of current increases, heat is generated in a wire. If too much heat is generated, a wire will soften and melt causing a failure. It is on this principle that a fuse works. The gauge (diameter) of the wire and the material of construction determine at what current flow (amperage) the wire will fail. All fuses are rated in amps (A) or the maximum current it can sustain before failure. The amperage rate will be clearly displayed on the fuse. Some fuses are designated as slow blow. This means that they can sustain a higher than normal

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current flow for a short time (such as when the power is turned ON). You will typically find slow blow fuses on power supplies and if you need to change one, be sure to match the bad one.

Fuses

The best way to test a fuse is to remove it from the device or circuit and test for continuity. Often if a fuse undergoes a catastrophic failure, it will be burnt or discolored. These are the first indications that a fuse may be bad.

Rectifiers

Rectifiers are circuits made up of two or four diodes. They are commonly used inside power supplies and voltage regulators to convert AC into DC. Since diodes will only pass current in one direction and AC current cycles from positive to negative, the effect of diodes is to pass current during only one half of the cycle. By connecting two diodes to a 120 VAC wire (one in each direction), the output will be 120 volts pulsating DC. Two diodes produce half wave rectification and four diodes produce full wave rectification. The four-diode configuration is often called a bridge rectifier. With additional circuitry, which includes capacitors and coils, the output can be smoothed into pure DC. The following is an example of a half-wave rectifier.

Half-Wave Rectifier

Transformers

A transformer is a metallic core wrapped with two or more coils of wire. Each wire has a different number of turns (wraps). By passing a current through one of the coils of wire, a magnetic field is generated. Current is then passed from one coil to the other via induction. Depending on the number of wraps, a transformer can “step up” or “step

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down” voltage. The ratio of the number of wraps determines the difference between the input and output of the transformer.

The input side of the transformer is called the "primary” and the output side is called the "secondary.” Computer transformers typically have one primary coil and three secondary coils. The secondary coils output the two 12V and one 5V outputs.

Transformer

Transformers are no more than a coil of wire therefore testing is simply looking for opens or shorts. By using the ohm function of a multimeter, you can check each wire of each coil for continuity. The best method for testing is to remove the coil from the circuit board to eliminate any erroneous readings caused by other components. Also, if there are any electrolytic capacitors they may discharge during your test giving you a false reading. When testing with the transformer in place, you will be able to determine if it is bad, but not necessarily, if it is good. A good transformer will show a reading of low resistance. No reading at all will indicate that the coil is open.

Transistors

The invention of the transistor revolutionized the electronics industry. They turned large power consuming, and temperamental, vacuum tubes into small power efficient and reliable devices. Transistors work like two diodes in series with an electronic switch connected between them. Physically, they look like a small plastic cylinder with three wires. The three wires are labeled E for emitter, B for base and C for collector. The wire labeled B is used as the switch. By supplying a small voltage to this wire, larger voltages can be controlled across the emitter and collector. This makes transistors ideal for use as amplifiers.

Transistors

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Note: Integrated circuits are made of thousands of miniature transistors, diodes, capacitors, and resistors combined into one package.

Static Electricity and a Computer

Electro-Static Discharge (static electricity) is one of the most damaging phenomena that occur with electronic equipment. ESD destroys thousands of circuit boards a year. Fortunately, it is one of the easiest things to protect against. Understanding ESD and how to prevent it is an important part of being a computer technician.

High voltages generated by electrical and electronic equipment are capable of doing severe damage to humans. So, it is with uncontained high voltages and electrical and electronic equipment. We have all seen what a short circuit can do to electrical equipment (smoke, fire and destruction). There is an unseen (and sometimes unheard) force that is just as deadly to a computer. That force is electro-static discharge created by humans. If not controlled (prevented), ESD can turn normally good parts into bad parts.

Static electricity is generated when two dissimilar materials are rubbed together. The rubbing causes positive electrons to migrate to one material and negative electrons to move to the other. When the materials are quickly separated (before the electrons have time to neutralize), one becomes positively charged while the other becomes negatively charged. The two materials are now electrically unstable and will discharge its energy to ground as soon as there is an available path (a conductor) for the flow of electrons. The discharge of this energy is Electro-Static Discharge (ESD).

There are two important points that you need to remember about ESD. First is that low relative humidity increases the possibility of generating ESD. This is particularly true in the low humidity environments caused by dry heat during the winter. The second is that ESD does not have to be seen to do damage to electronic components. It generally takes a potential of about 20,000 volts before we will actually “see” or “feel” the discharge, voltages of less than 100 can be fatal to some components. While it is generally accepted that humans can accumulate voltages of 25,000 or more, it is the smaller charges, that cannot be felt, that do most of the damage to semiconductor devices. The simple act of improperly handling memory chips can damage them without us even knowing what happened.

The best ESD defense is prevention.

Preventing Static Electricity

Understanding the source is the first step in prevention. Improper handling is the number one cause of ESD damage. When you purchase new memory modules or a hard drive, you may notice that they are packaged in a special bag. These are called anti-static bags and are designed to prevent ESD. As a computer technician, you should save a few of these bags, just for storing electronic components temporarily while you are working on a computer.

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The answer to ESD prevention is to maintain all components and yourself at the same electric potential - GROUND POTENTIAL. As long as you make sure that you are discharged before you pick up any electronic parts, you will not have any problems with ESD. The electronics industry has designed and approved several devices you can use to prevent ESD when working on electronic equipment. Several techniques can be used to prevent ESD. The following are some guidelines:

• Do not wear clothes made of synthetic materials.

• Use an ESD wrist-strap. Be sure that you are using it properly and that the resistor is good. Connect the clip to the computer chassis.

• Make sure that the computer chassis is grounded.

• Keep electronic devices in the protective bags until needed. You can use the bags to lay the parts on after removing them from the computer.

• Do not place circuit boards on metal or foil.

• Create an ESD workstation – anti-static mat, wrist strap, ground wire.

• Maintain the relative humidity between 50 and 70 percent.

There may be times when you do not have your tool kit with you and you need to make a repair. The best way to eliminate any static charge is to ground yourself to the chassis of the computer. By simply touching the frame, you will discharge any built-up ESD. As long as you and the computer are at the same potential, it should be OK. Always touch the chassis before picking up any parts or removing parts from the computer.

Electricity and Safety

Computers are electronic equipment and therefore consume electricity. Although most of a computer uses safe 12 and 5 volts DC, the main power source and the monitor use high voltages.

ELECTRICAL SAFETY IS YOUR RESPONSIBILITY!

Standard outlet voltages in the US provide a nominal 120 VAC at 15 to 20 amps. It is possible to receive a lethal shock from much lower voltages than these. Inside a computer (especially the monitor), voltages as high as 30,000 volts (30 KV) may exist (even after the power is turned OFF).

It is vital to follow basic electrical safety guidelines when working on computers. There is no substitute for good old common sense. However, here are a few tips:

• If in doubt - don’t! If you are not sure, then you are probably wrong. Remember Murphy?

• Always use grounded outlets and power cords.

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• Switch OFF and disconnect all equipment from its power source before removing any covers.

• Always replace blown fuses with the correct rating and type.

• Do not work alone - you might need help in an emergency.

• Remove all jewelry - these are conductors and can cause short circuits.

• Computer power supplies and monitors use and store potentially lethal voltages (often for days or longer). Only trained personnel should service them.

• Work with one hand. Using two hands can cause a direct circuit, via your heart, from one object to another.

In the US, common AC wiring uses the following colors:

Standard Wire Color Codes

Connection Color

Live or HOT Black

Neutral White

Ground Green or Bare copper

Protection from Environmental Hazards

The proper placement or location of a computer relative to its environment is important for ease of maintenance and long life. This will also minimize the requirements for cleaning. Let’s review good practices for placement of computer equipment.

• A dust-free and smoke-free environment.

• Controlled humidity (50 to 70 percent relative humidity).

• Controlled temperature (do not place too close to a heater or in direct sunlight and avoid temperature extremes).

• Good ventilation (make sure that the fan/ventilation vents aren’t blocked).

Note: BE CAREFUL - color-codes for AC wires and DC wires may be different. Example - the ground wires on the connector for a motherboard are black.

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Generally, the office environment is ideal for computers. However, there may be situations that require computers to be in less favorable environments. Should you encounter one of these you will have to take special precautions. First, you will need to increase the frequency of inspections and maintenance. Secondly, you may have to provide some extra protection. For example, computers in a laboratory environment may require plastic covers to prevent chemicals from being spilled into the keyboard. For computers that are located in industrial environments, especially, those that are corrosive, you may have to enclose the computer and peripheral equipment in a special cabinet and provide it with its own fresh air supply.

Computers and their peripheral devices are electronic equipment; therefore, they must safety issues related to power. However, when working on this equipment there are several other issues besides electrical that you must take into consideration.

Weight

Some of the equipment such as printers, monitors, and even the computer itself can weigh several pounds (10 – 20). This may not seem like much; however, if improperly picked-up (or dropped) they can lead to back or other injuries. Be especially careful when removing them from their original packaging. These components are generally packaged very tightly to provide protection during transport and can be difficult to remove.

Cuts

Be very careful when removing covers from computer components. The frames of the cases are often made of thin metals with sharp edges. Also, poorly cut or stamped parts can still have metal burs, which are very sharp. Devices such as scanners and monitors have glass components that can break.

Trip Hazards

Being electrical and communication devices, computers tend to have many cables and wires. If not properly installed, these wires and cables can constitute a serious trip hazard.

When installing or working on any equipment, make sure that the work conforms to all local and national safety codes, such as OSHA (Occupational Safety and Health Administration) and NEC (National Electric Code) standards. Also, most companies have their own safety department and safety manual. Be sure that you are familiar with them as well.

Voltage Hazards

Power is the number one safety hazard encountered when servicing a computer. Here are some guidelines when working with electrical devices and components.

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ESD

The number one electrical concern when working with computers is ESD (Electrostatic Discharge). Remember, ESD won’t hurt humans, but it will destroy sensitive computer parts even when we don’t feel the discharge. If proper ESD tools are not available, touching the case (specifically, the power supply) while working on the computer or its components will provide some protection. This will only work if the power supply is plugged in to a properly grounded electrical outlet.

Grounds

The term “ground” when used with electronic equipment, can be confusing. A ground is any point from which electrical measurements can be referenced. In most cases, ground refers to an Earth Ground. With early electrical systems, the earth was used as a path for current to return to its source. This is why telegraphs required only one wire. In most instances, the frame of the computer is at ground potential or earth ground (as long as the power cord is installed and connected to a properly grounded system). Some electronic equipment uses a special path or conductor for its ground. This is known as Signal Ground.

Electronic equipment is both susceptible to and a source of EMI (Electromagnetic Interference). A properly grounded computer will both prevent the transmission of EMI and protect itself from other sources of EMI. Unchecked EMI will distort images on a video display, corrupt communications equipment, and corrupt data on floppy disks.

High Voltages

For the most part, a computer uses ± 5 and ± 12 volts DC. However, two places use much higher voltages.

The power supply uses 120 VAC. This voltage is found inside the power supply case. In most cases, there is no need to open the power supply case to work on the power supply. The cost of a new power supply is low enough that it may be easier to replace than repair. However, should you decide to open the case, BE CAREFUL. Remember, the power switch, usually located on the front of the computer also uses 120 VAC to turn the power supply on and off.

Monitors use very high voltages (up to 50,000 Volts) to drive the CRT. Working inside the monitor case should be left to a properly trained technician with the necessary tools to deal with these voltages.

With these two exceptions, there are generally no electrical hazards inside a computer. Here are some guidelines when working around computers:

• Never wear jewelry or other metal objects when working on a computer. These items pose an electrical threat and can cause shorts that will destroy components.

• Never have liquids around electrical equipment.

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• Do not defeat the safety feature of the three-prong power plugs by using two-prong adapters.

• Replace any worn or damaged power cords immediately.

• Never allow anything to rest on a power cord.

• Avoid using extension cords. They can become trip or catch hazards. Also, they may not be rated to carry the current requirements of your system.

• Keep all electrical covers intact.

• Make sure all vents are clear and have ample free-air space to allow heat to escape.

• Some peripheral devices such as laser printers and scanners may use high voltages. Before removing any covers or working on any of these devices, be sure to read the manufacturers manuals.

ELECTRICAL SAFETY IS YOUR RESPONSIBILITY!

Fire Safety

Fire is something that we don’t like to think about. However, it is a fact of life. A fire in the workplace can be disastrous both in terms of lost equipment and injuries to people. Knowing what to do in the event of a fire can save valuable equipment and most importantly, lives. Here are a few tips to help prevent fire and to protect yourself:

• Always know the emergency procedures for your company.

• Know the location of the nearest fire exits.

• Know the location of the nearest fire extinguishers and how to use them.

• Don’t overload electrical outlets.

Simply knowing the location of a fire extinguisher is of no value unless you know how to use it. If you don’t, contact your safety department or your local fire department. They will be glad to see that you get the training you need. Also, remember that using the wrong type of fire extinguisher on a fire can be worse than not using one at all.

There are three basic types of fire extinguishers:

Fire Extinguisher Types

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Summary

In this chapter, we discussed the principles of basic electricity and the methods for testing computer components. We also reviewed the procedures for staying safe in a computing environment, both for you and the computer equipment.

• Ohm’s law is the basic formula for power calculations.

• Ohm’s law states that the current flowing through a conductor, or resistance, is linearly proportional to the applied potential difference (volts).

• There are two types of power: alternating and direct current, (AC and DC).

• A multimeter is a key tool of the Computer Technician and is used to measure volts, continuity and resistance.

• A Computer Technician should be familiar with the various electronic components found on a circuit board.

• ESD damages computer components.

• ESD can happen without detection.

• ESD can be prevented.

• Electro-Static Discharge (ESD) is created by the heat of the friction created by the sudden separation of two dissimilar materials. ESD can cause damage to computer parts. Always take ESD preventative measures when working around a computer.

• Electricity is delivered to our homes and businesses as AC (Alternating Current). It is converted to DC (Direct Current) for use inside a computer.

• Electricity always seeks the path of least resistance to ground. An electrical outlet or an extension cord without a ground wire is unacceptable for use with a computer.

• It is vital to follow basic electrical safety guidelines when working around electronic devices. Remember electrical safety is your responsibility!

• Know what components of the computer present the most risk of electrocution.

• Know your fire extinguishers – what type to use in a given situation, where they are located, and how to use them.

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KEYWORDS Exercise

Define each of the following keywords. Hint: There’s a glossary in the back of this book.

Keyword Definition

AC

Ampere

Capacitors

Coil

Diode

DC

Electricity

Electro-Static Discharge

Fuse

Ground

Hot to Ground Test

Hot to Neutral Test

Impedance:

Multimeter

Neutral to Ground Test

Ohm

Ohm’s law

Power

Rectifiers

Transformer

Transistors

Volts

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Review Questions – Chapter 3

1. What is Ohm’s law?

2. What is the formula for Ohm’s law?

3. What is the difference between AC and DC?

4. What instrument is used to measure the various components of electricity?

5. How do you test for continuity?

6. What is “AC Ripple” and how do you test for it?

7. Describe ESD and how to prevent it.

8. When working with a computer, when is it acceptable to use an AC power supply that is not grounded?

9. Why is ESD dangerous to computers?

10. Will a properly grounded computer help prevent EMI?

11. Name some safety precautions you can take to protect yourself from High Voltages while working on a computer.

12. What type of fire extinguisher is used for an electrical fire?

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Chapter 4 – Motherboards and Processors

This chapter begins with the motherboard—the centerpiece of the computer. The motherboard is a large circuit board (also known as a PWB or printed wiring board). Its purpose is to support the CPU (Central Processing Unit) and all of its associated chips (the chip set) and to connect them to the rest of the system. It is also responsible for managing the system buses that, as we mentioned before, move data between the CPU and other components inside the computer. Of all the hardware found in a computer system, it is the motherboard that is the center of activity. All devices in a computer are in some way connected to the motherboard.

There are various types of motherboards and each motherboard has certain specifications that will allow you to uniquely identify it. Here’s a chart to help keep them straight:

Motherboard Types Defining Features

AT The processor slot or socket and memory sockets are located at the front of the motherboard with longer expansion cards to extend over them.

ATX Integrated I/O port connectors and PS/2 mouse connector.

Soft power support and 3.3v power support.

Intel only uses ATX form factor.

Baby AT Used for 486 and Pentium processors.

The processor slot or socket and memory sockets are located at the front of the motherboard with longer expansion cards to extend over them.

Usually has a full-sized keyboard connector soldered onto the board.

LPX Uses a riser card.

Goes into slimline or low profile cases.

Integrated video card.

Mini ATX Integrated I/O port connectors and PS/2 mouse connector.

Soft power support and 3.3v power support.

Intel only uses ATX form factor.

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Motherboard Types Defining Features

Mini LPX Uses a riser card.

Goes into slimline or low profile cases.

Integrated video card.

NLX Evolved from the LPX form factor and still uses the riser card.

Uses DIMM memory and AGP cards.

Cooler than the LPX form factor.

XT Motherboard

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AT Motherboard

Baby AT Motherboard

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ATX Motherboard

Micro ATX Motherboard

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Flex ATX Motherboard

LPX Motherboard

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Mini-LPX Motherboard

NLX Motherboard

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The Computer Case

No discussion of motherboards can be complete without first talking about the computer case. Most components that are assembled within a computer will fit into almost any case (there are some proprietary designs that limit what hardware can be installed), however, the case and the motherboard design are interrelated and must be specified to work together. Although the motherboard is a sub-assembly of the case, they are often considered one and the same.

Computer Case - tower

The case is more than just a “box” to house a computer. It is often the identity of a specific brand of computer, and sometimes even the reason why we purchase a particular computer. After all, we do want something that looks good, especially if we spend a lot of money on it. The early cases were just boxes that sat on the desk and held the computer’s monitor. Often they took up the entire desktop, so some users built stands and put their computers on their side under the desk. That idea was so good that manufacturers began to build computers that sat on their side; they called them “towers” and of course, raised the price. Some manufacturers today build “designer” computers in a wide array of colors, which are meant to appeal to the consumers’ taste.

Computer Case – desktop version

From a technical perspective, the case is just a plastic or metal box that houses the computer hardware. The main ingredient in the box is the motherboard, which contains the CPU and other primary components that make up a computer. A good case, either plastic or metal, will be designed to act as a shield for EMI (electromagnetic interference). This will prevent, or at least reduce, the amount of electrical “noise” generated by the computer from escaping into the environment. This noise potentially causes interference with other electronic equipment. It is not a good idea to run a

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computer for extended periods with the case open or removed entirely. Not only can this release EMI, but it can also impede proper airflow and cooling of the components.

Electromagnetic interference (EMI) is the same as Radio Frequency Interference (RFI), but EMI is a newer term. EMI is considered any radio frequency that is emitted from an electrical or electronic device that is harmful to the surrounding equipment, or interferes with the operation of another electrical or electronic device. For example, if you had a fan and computer in close proximity and you noticed wavy lines on your computer monitor when the fan was running, but not when it is off. This would be a result of EMI. Also, a computer with poor EMI shielding will cause interference on a TV screen or telephone. Any high-quality computer will contain special circuits and grounding to prevent emissions into the surrounding area. Running a computer without its cover is a sure source of electromagnetic interference.

As a computer technician we usually don’t concern ourselves with the computer case, we deal with whatever our customer already has. However, when it comes to recommending a computer for purchase, the size and configuration of the case should be considered. Depending on the business application, the difference between a tower and a desktop model could be important. There are two general rules to follow when considering the case:

• The bigger the box, the more components it can hold (the greater the expansion potential), and the better the airflow (essential for internal cooling). Large cases are easier to work with.

• The more compact the box, the less expansion potential it has; working on it is much more difficult and airflow is reduced. However, it is easier to find a place for it.

Modified Cases

Nowadays, it is possible to modify the look of your case or purchase a case that has been modified. Some modified cases have clear sides, some cases have unique paint jobs, and some have room for more drives. Those who prefer modified cases generally prefer other modifications also. Those modifications can include neon lights, extra fans, water-cooling, and wire loom (covering for power cables).

Components

The motherboard is the computer. Look at the following picture. You will see a basic motherboard. It contains many components that we will study in detail as we progress through this course. You may also notice many small components such as resistors and capacitors. These small components are not very important to us, but are used to insure that the key components are supplied with the necessary voltages to work properly.

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Typical Motherboard

The motherboard and its associated components define the limits for speed, memory, and expandability of the computer. The motherboard is the main circuit board found inside the computer case. The CPU is the central component of the motherboard. In addition to being equipped with an assortment of CPUs, motherboards come in a variety of shapes. Before installing a new motherboard in an older computer, pay careful attention to size and location of mounting holes, because one size does not fit all. The location of the motherboard inside the case is of no real consequence as long as it fits, receives sufficient ventilation (for cooling of the CPU), and does not conflict with other hardware. The first generation of Pentium chips required a cooling fan to be installed on top of the chip and connected to the power supply. The new Pentium II and III chips come with the cooling fan as part of the package. A faulty cooling fan can cause damage to the processor and system lockups. When considering the purchase of a new motherboard, keep these things in mind:

• Most “generic” motherboards will fit into “generic” computers. One good reason to consider purchasing a computer clone is that it is easier and typically less expensive to upgrade.

• Brand-name manufacturers don’t want users swapping their motherboard for other manufacturers’ motherboards or clones. If you have a brand-name computer, you may be required to purchase a new motherboard from the same manufacturer.

• Before you buy, check technical references to be sure that the new board will fit. Often this information can be found in the owner’s manual(s). If not, check the manufacturer’s Web site, if available, or check a source such as the MicroHouse Technical Library. The MicroHouse Technical Library is not free, but it is a comprehensive source. There are many other sources available on the Internet for technical information as well.

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• For all practical purposes, you cannot repair motherboards. The time and technical skills required often do not justify the cost. They should be replaced if physically or electrically damaged.

• Since it is the most expensive and difficult part of a system to replace, check all other internal and external components before removing or replacing the motherboard. In other words, make sure that the problem is the motherboard first.

Chip Set

The main features of a motherboard include the computer chips or microprocessors on the board. Yes, there are a lot of wires and connectors, but the IC (Integrated Circuits) chips work in harmony to give the motherboard its identity. While there are many components and integrated circuits (IC chips), a special group works together to support the CPU. These special chips constitute the chip set. These chips are highly complex and coordinated ICs (integrated circuits) that help the CPU manage and control the computer's system. Early motherboards contained many different chips, each designed to control a specific portion of the computer. For example, the 8088-chip set consisted of 6 chips to support the CPU. As chip technology improved, the number of chips were reduced as more and more functions were integrated into single chips. Today’s motherboards have a few highly integrated chips. Fortunately, for computer technicians, we do not have to know all the different chips and their specific functions. We need to focus only on one, the CPU. When replacing a CPU, you can’t go and purchase just any CPU. You must purchase one that is compatible with the motherboard and the other chips on it. If not, the computer won’t work. A basic chip set, whether one or ten chips, provides many functions:

• Bus Controllers

• Data and Address Buffers

• DMA and Interrupt Controllers

• Peripheral Controllers (hard drives, floppies drives and CDs)

• ROM/BIOS

• Any other chips specific to the design.

Note: You may not understand all of these terms at this time, but you will by the end of the course.

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Motherboard with Chip Set

These chips define the specifications for the motherboard. As we begin to identify and categorize motherboards and computers, we will actually be describing the limits of the chip set on board. In addition, when it comes time to upgrade, it will be these chips that determine just how far you can upgrade before being required to replace the motherboard itself.

ROM – Read Only Memory

Anyone who has ever worked with computers knows one thing: there is never enough memory. Later in this course, we will be discussing the memory of which you never have enough. That memory is called RAM or Random Access Memory. On the motherboard, and most other computer devices as well, are some special memory chips called ROM (Read Only Memory). These chips contain special memory that is permanent – it cannot be erased. The function of the data stored on these chips is to provide special information for the CPU when it needs it. When stored in ROM, information that is required to start and run the computer or a device cannot be lost or changed. The downside of storing data in ROM is that we have to change a chip to update information.

Systems that are more recent use a technology called flash ROM that allows ROM chips to be updated by software available through the motherboard or device supplier. Check the Internet site for the supplier (software and instructions are generally downloadable) if you suspect your ROM chip has flash ROM technology.

PROM & Firmware

PROM (Programmable Read Only Memory) is ROM that can be initially modified. A special machine called a PROM Programmer is used to tailor a microcode program. Since this leaves no margin for error, most programmable chips today are Erasable Programmable Read Only Memory (EPROM).

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Firmware is the programming that is inserted into PROM that then becomes a permanent part of a computer. Firmware is sometimes distributed for printers, modems, and other devices.

BIOS

BIOS (Basic Input/Output System) is a set of procedures stored on a ROM chip. This data is the information that a CPU needs to communicate with the most basic of hardware components on or connected to the motherboard. It stores the data to run the keyboard, communication ports, and drives. Without this basic information, the CPU will not be able to boot or start up.

One of the fixes for the Y2K problems for some computers was to upgrade the BIOS with a version capable of handling the new date parameters. Upgrading the BIOS requires that you know the make, model, and contact the manufacturer for an appropriate update.

The ability to upgrade a computer provides flexibility and keeps the cost affordable for most of us. It also allows us to keep a machine in service for longer periods before requiring replacement. The purpose of the ROM chip that contains the BIOS information is to maintain the specific information for the hard drives, floppy drives, and memory. This would mean that every time you needed to install a new drive or upgrade an old one you would have to replace this chip. To overcome this problem, a special ROM chip called CMOS (Complimentary Metal-Oxide Semiconductor) is used to hold this upgradeable data. It does not hold all the information, only the information that is most likely to change.

On newer computers that use plug and play technology, the data for a device is stored on the device itself. When the computer is booted, it searches the system and collects the information from the device. This, for the most part, eliminates the need for CMOS. The CMOS chip also maintains the date and time information when the computer is powered off. Even though plug-n-play technology has diminished the requirements of CMOS, there is still some information stored in CMOS, and since there are still a lot of old systems out there, you as a computer professional will need to understand how to change the information in these chips.

If the setup or hardware information is different from what is on the system, the computer won’t work. For example, if the hard drive information is incorrect, the computer can be booted from a floppy disk, but the hard drive may not be accessible. You may have to manually enter the date and time information.

The information contained in a CMOS chip will depend on the manufacturer. Typically, CMOS contains at least the following information:

• CPU and memory size

• Date and time

• Floppy and hard drive disk types

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• Optional password for security for startup and system setup

• Serial and parallel port information

• Video information

Unless your system utilizes plug and play, you will need to make changes to your CMOS setup anytime you upgrade or change any of your system’s hardware. This is because the CMOS settings must accurately reflect the hardware types on the system in order to function. If the data in the CMOS does not match the hardware, you will get an error and will not be able to boot the computer.

To make changes to a CMOS chip, you’ll need to run a CMOS setup program. The way to start this program depends on the manufacturer of the BIOS, and not the manufacturer of the computer. Manufacturers of motherboards purchase the BIOS from other companies, most of which specialize in making these chips. Many different computer suppliers use the same BIOS while others customize their BIOS to have the look of their product. The BIOS manufacturer and version number is the first thing you see displayed when you boot up your computer.

Many different companies write BIOS code and sell it to motherboard manufacturers. However, the three most common BIOS manufacturers are AMI, Phoenix, and Award. If you would like to know the BIOS manufacturer for a particular machine, start the computer and when the first text appears on the screen, press the ”Pause” key in the upper right of your keyboard. This will pause the program (the BIOS program as it loads and runs) and allow you to read the splash screen for the BIOS. For example, Award is a popular BIOS manufacturer.

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If you boot an Award machine, you will see a screen similar to the following:

Award Modular BIOS v4.51PG, An Energy Start Ally

Copyright © 1984-97, Award Software, Inc.

05/22/1998 For Apollo VPX/97 PCIset

Award Plug and Play BIOS Extension v1.0A

Copyright © 1997, Award Software Inc.

Press DEL to enter SETUP

You will notice, that at the bottom of the screen, it says “Press DEL to enter SETUP”. This message tells how to access the BIOS setup program. Most of the manufacturers will tell you how to enter their setup program. Usually, you will have to be quick because the message will flash past. In this case, you would press the DEL. Some manufacturers will use CRTL ALT ESC or some other combination of keys to access the setup utility. If the keystrokes are not displayed, you will have to rely on the documentation that came with the motherboard, or open the case and look for the BIOS chip on the motherboard (it should have a label) and then contact the BIOS manufacturer.

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A typical CMOS setup

Phoenix is considered a manufacturer of high-end BIOS and was the company who originally developed BIOS. To enter a Phoenix BIOS utility program, use the F2 key. Let’s look at some typical screens from a Phoenix BIOS setup program.

This figure shows the first screen of this CMOS setup. From this point, you can select alternate pages (Advanced, Security, Power) or adjust any of these individual items: floppy drive, hard drive, date/time, and RAM settings.

Main screen

The Hard Drive setup screen is where individual hard drive settings are selected.

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Hard drive setup screen

The Advanced screen leads to more advanced setup parameters. A lot of customization can be done with these settings. Pay careful attention to any warnings before making any changes to your device settings.

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Advanced screen

The Security screen allows you to set security parameters. Be careful: once you set a password, you have to remember that password to change it.

Notice that the virus check is disabled. Windows 95/98 does not like CMOS virus checkers. Turn off the virus check setting if you are trying to install Windows, you are certain no virus software is on the computer, and you keep getting an error warning you to turn off all anti-virus software.

Tip: These built-in CMOS anti-virus protectors actually do very little to protect your system. For the best possible protection from viruses, be sure to install a good anti-virus program, keep it current, and avoid suspicious floppies and downloadable files.

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Security screen

Tip: If you don’t remember a password, you can usually remove it by erasing the entire CMOS setup. Check the motherboard owner’s manual for the correct procedure. Be aware, you will have to reinstall all the CMOS settings before continuing.

The Power screen allows the user to set up any power conservation options provided by the manufacturer. These features typically include setting a time limit for reducing power to the monitor and hard drive.

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Power screen

BIOS Configuration

If you have ever turned on a computer and all of the sudden for no apparent reason, it is unable to detect your hard drive or floppy drive; you are most likely experiencing a loss of your BIOS configuration. While this can be very upsetting, it is usually easy to correct and is often an indication of other problems. If the BIOS is lost during an update where the power goes out, it could cause motherboard failure. Most problems involving CMOS are configuration errors. This means that the BIOS and the hardware configurations do not match. In most cases, you will be given a message and asked to Press F1 or some other key to continue. This will then take you directly into the setup utility. In other cases, nothing will happen. Some BIOS’s will automatically run the setup utility any time there is a problem. The message that you see usually uses the word mismatch and will be similar to one of the following:

• CMOS configuration mismatch

• CMOS display mismatch

• Memory Size mismatch

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The most common cause of this failure is the loss of the CMOS battery. If you notice that every time that you start your computer, the date and time is wrong, or you are asked to enter a new date and time before the computer will boot, then the CMOS battery is most likely is weak and failing. Checksum errors and mismatch errors can also be caused by a failing battery. So, if you every forget your BIOS password, remove and reseat the battery or short the CMOS jumper.

Note: If a setting changes, it is most likely the symptom of a failure rather than the cause of a failure. If, after correcting the setting, the failure comes back another day, the problem is most likely not the CMOS but something else that is causing it to change.

There are many reasons that a CMOS can unexpectedly change. Most usually occur right after hardware has been replaced or serviced. Here are but a few:

• A new device was installed that conflicts with an existing device. Example, installing a second hard drive.

• Expansion cards have been removed or inserted. This could cause an electrical surge, or it may not be properly inserted, and the BIOS can’t find it.

• Improper handling of the motherboard can cause electrical short circuits or failure due to ESD. It can also cause disconnected or loose cables.

• Even installing software such as a new operating system can cause CMOS problems (this happened to me when I upgraded to Windows 95 on a computer with a proprietary motherboard).

It is wise to back up the CMOS setup just as you do with other important data. For example, print out the screens or write it down (especially before making hardware changes). Another good way to save BIOS information is to open the setup utility and use the print screen command. This will copy the information to a printer. There are many third party CMOS save and restore utility programs available. Check with your local computer store or check the Internet.

Keep in mind that the BIOS might need to be updated whenever you install a new piece of hardware, such as a faster CPU or a plug-and-play peripheral. Also, the BIOS is the place to change the boot order of the devices in your computer, that way, if you want to bypass one of those devices, like the hard drive, you can set it to the last device the computer will go to for a bootable source.

Note: With Windows 95/98 and Plug and Play, many newer machines place less emphasis on the CMOS. The BIOS information is stored with the device and is automatically detected at boot.

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The Motherboard Battery

The CMOS chip contains volatile data. That is, data that is subject to change just like the data stored in the working memory of a computer. As we all know, when we turn off our computer, all the data in memory disappears. To prevent the same kind of loss of the BIOS data, a battery is installed on the motherboard that maintains a small amount of voltage to the CMOS.

One of the pieces of information that is kept by the CMOS is the current date and time. Just like a battery operated alarm clock, as the battery weakens, the time slows down. As technicians, we can take advantage of this to monitor the strength of a CMOS battery. If you notice that the time needs to constantly be updated, it is more than likely time to change the battery.

In most instances, you will be able to detect a weakening battery by monitoring the date and time. However, often we do not pay attention to the time and the battery fails as described before. When a battery is truly dead, you will not be able to reboot the system without having to run CMOS setup every time. In most cases, the battery just becomes weak and after rebooting, receives enough of a charge to keep going for a while. You may be able to run successfully all week, but the computer will not boot after sitting off for a few days. Replacing a battery is an easy task and should be done any time that it is suspect.

The actual battery and procedures for replacement depends on the design of the motherboard. Since each supplier uses their own preferred design, you should always check the specifications before replacement. There are however, a few things to consider:

• Batteries can be either internal (on the motherboard) or external (in a battery pack).

• Internal batteries are often mounted in a compartment so that they can be replaced similar to a watch battery.

• Some, but not all, motherboards have an installed capacitor that will maintain a charge to the CMOS while you replace the battery thus preventing the BIOS information from being lost.

• Some batteries are soldered in place and require extra work for replacement.

• Some motherboards have terminals so that an external battery can be installed to replace the internal one.

Not all motherboard batteries are equal. The voltage of CMOS batteries ranges from 3 to 6 volts. You will need to check the motherboard or the motherboard documentation to determine the actual battery requirements. The 3-volt lithium watch battery is becoming very popular with motherboard suppliers. Many of these are mounted in a special holder so that the battery can be easily changed, however, some manufactures solder them in place.

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When replacing a CMOS battery, you should be prepared to re-enter all the data. While some CMOS chips contain a capacitor (acts like a battery for a short time -only a few minutes) that allows replacement of the battery without losing data, you cannot always count on it. If the motherboard has a soldered battery, you will need to look for a connection that will allow installation of a second battery. The best source of information about replacing a CMOS battery is the documentation that comes with the motherboard.

Start-up Test

Every time a computer is turned on or re-booted it goes through a procedure of self-diagnostics. This test is commonly known as POST or Power On Self Test. This is a low level test and the only purpose is to confirm the basic hardware components of the computer (the bare minimum hardware requirement is a processor, some RAM, and a video card). It does not guarantee that the operating system or software will work because it happens before any software is loaded. For example, it will test the power supply to ensure that sufficient power is available to run; it will test to make sure that a monitor is connected. It will test for drives, it will test for a keyboard, and it will test for memory errors. If errors are encountered, it will issue an error warning to the operator. Problems that occur after this cannot be detected by POST, such as memory failure.

Note: With reliance on plug and play technology hardware increasing rapidly, the emphasis on POST codes is rapidly diminishing. However, this subject remains an objective of the A+ Certification exam, so we will cover it.

When the POST test encounters a problem, it will report the error by either an audible alert (a beep) or by displaying a text message on the monitor screen. Resetting the BIOS or checking and replacing faulty hardware can reduce errors from POST.

The POST test is conducted in two phases. The first phase takes place before confirmation that the monitor is working. During these tests, any errors will be reported by an audible alert. Just to make sure that the speaker is working, the POST will test it by sending it a single beep. If you don’t hear a beep, the speaker may not be working.

If all is well during the first phase (the monitor is confirmed to be functioning), the POST will continue to check the hardware and will report any errors by displaying a text code on the monitor screen.

Unfortunately, these error beeps and messages are usually not specific enough to tell you what the problem may be, but only what general component has a problem. POST codes may have different meanings from different manufacturers.

If you get a beep code, you should refer to the manufacturers documentation for proper identification and troubleshooting practices. If you don’t have access to these documents, troubleshooting after a beep code error can be somewhat challenging. First, the fact that you must respond to a beep code means that the boot cycle has not progressed far enough for the monitor to work, therefore, you will not receive any visual codes to help identify

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the problem. The good news is that since you have not progressed far enough for the monitor to work it limits the problems to a select few.

• BIOS Chip

• DMA Controller

• Interrupt Controller

• Memory – ROM

• Power Supply

• Processor

• Video Card

• Video Cable

Knowing this, a simple process of elimination will usually solve the problem.

If the power supply is bad, you most likely will not even get started. No lights will come on and no activity will be heard from within the computer case. Remember, this may also mean that the computer is not plugged in or that the power strip is off.

If the problem is in the DMA controller, interrupt controller, BIOS chip, or processor, you most likely have some serious motherboard problems. Replacement is probably the only recourse. Often these chips are soldered in place making them very difficult to replace. A new motherboard may be a more cost effective solution.

This leaves either the video card or the memory. The most likely cause of either of these to fail especially after working inside the case is a loose card or memory module. Do not forget to check the video cable. A loose or disconnected cable to the monitor will probably cause a beep code more than anything else.

Instead of beeps, POST will display either text or numeric error messages on the screen once it has performed the video test. BIOS programmers in the early days were restricted by the amount of memory space available in the chip. In order to simplify error generation, a common set of numeric codes were used to identify various problems within the boot process. Service technicians needed to have a list of these codes and their interpretations. Often, this required obtaining a list from each BIOS manufacturer used, in addition to the standard ones.

As the memory limits for BIOS data increased, these codes have been replaced with error messages such as: “primary hard disk failure”, which could mean that the hard drive is fried, a cable is loose, or simply that the CMOS settings are incorrect. In any case, this type of error messages is much more user friendly than a “602” at the top of a blank screen, which would mean the same thing.

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As a PC technician, (not to mention at the A+ Exam) you may run into some of these older BIOS codes, so we have included the following table of common error codes:

161 – CMOS battery failure

301 – Keyboard error

501 – Memory failure

602 – Floppy Drive failure

1302 – Joystick failure

Note: keyboard errors are a result of stuck keys or an unplugged connector, which causes an annoying continuous beeping noise.

In most cases, BIOS manufacturers have categorized their beep codes into groups based on possible problems. While the following table may not represent all manufacturers, it will help when troubleshooting an unknown system.

Common Beep Categories

Category Meaning

1xx System board

2xx Memory

3xx Keyboard

4xx Monochrome video

5xx Color video

6xx Floppy disk

17xx Hard disk

3xxx NIC card

When you encounter any of these messages, remember two things:

• Read the entire message – don’t assume that you know what it is.

• Don’t let the content of the message intimidate you. Programmers tend to write a limited number of messages and often use the same message for many different events. The message should lead in the direction of the solution, not necessarily give you the answer.

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DON’T FORGET TO WRITE DOWN THE MESSAGE ESPECIALLY ANY ERROR NUMBERS.

Bus Architecture

Unlike most industries, advances in the computer industry usually take place in technological jumps. It is not a slow process that evolves with time, but one that makes large incremental advances with the development of each new technology. For example, the development of the transistor and the microprocessor certainly revolutionized if not created the industry, as we know it today. One development that has established a measurement or benchmark for the progress of computers is the data bus. Earlier we discussed the concept of a bus in that it is a group of parallel wires on the motherboard. Expanding a bus from one wire to four wires, to eight and so on may not seem like much, but in reality, it has a significant role in setting the capabilities and limits of a computer. In the next section on microprocessors, we will see how it comes together, but first we must understand the computer bus. There are two buses that are important to us, the external data bus and the address bus.

A Computer Bus

Information is transmitted throughout a computer by using a bus and BINARY code. The external data bus is the primary bus for handling the flow of data. All devices that require the handling of data are connected to the external data bus. Everything in the computer that handles data is connected to the external data bus and therefore any information (data) placed on the bus is available to all devices connected to the computer. Early computers used 8 conductors (8-bit data bus) that allowed for the transfer of one byte of information at a time. As computers evolved, the external data bus increased to 16, 32 and now 64 conductors. These improvements allow larger and/or more “data” to be processed simultaneously. The following figure shows a CPU attached to its motherboard. The motherboard is the main circuit board that contains the external data bus. Notice all the other devices also connected to the motherboard and therefore the data bus.

A computer bus

To understanding how a computer works, think of each device on the data bus (including the CPU) as having an ON/OFF switch and a voltage meter connected to each conductor of the data bus. By turning the switches ON, the device can apply power to the conductors thus creating one byte of information (on an 8 bit bus) for all other devices to see. By “looking” at the conductors (like using a voltage meter to determine which ones have power and which ones do not), the device can read data. The following graphical shows a data bus with a CPU and a device connected.

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External Data Bus

The external data bus is the super highway for data in a computer. By applying a voltage, or by reading the presence of voltage on any of the conductors, communication will take place. Coded messages can be sent in or out of any device connected to the external data bus. The data bus is equivalent to a large party line.

REMEMBER!

EVERYTHING THAT USES DATA IS CONNECTED TO THE DATA BUS.

The size of the data bus (number of bits) will affect the speed of the computer. Typically, external data buses are defined in byte wide increments and each new bus is double the previous version. Four became eight that became sixteen and then thirty-two and now sixty-four.

An Address Bus

The function of the external data bus is to connect everything and to move data between the CPU and devices. It is truly one big party line. Moving data between devices is not so difficult. It simply requires that strings of data be placed on the data bus one byte at a time. On the other hand, a computer’s memory stores large amounts of data that is received from the CPU as well as from other devices. It is the CPU’s file cabinet. The question is, how does the CPU tell the memory chips when and what data to read or place on the data bus? To accomplish this, we need a second bus. This bus is called the address bus and its size determines the maximum amount of data that the CPU can store.

A portion of the CPU circuitry is used as a memory controller. It retains sole jurisdiction over the memory chips and tells them where to store each byte of data. It also tells them whether to read the data on the data bus or place data in its memory on the data bus.

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Before we can understand how memory is addressed, lets look at how a byte of data is stored in a memory chip. These chips are called RAM (Random Access Memory). This type of memory is called random access because the CPU can place or retrieve bytes of information from any location at any time.

Think of memory as a large array (the columns being individual bits and the rows containing 8 bits, or 1 byte of data). The following figure graphically shows an array containing “1s” and “0s”. Notice that each cell represents one bit of information and one row represents one byte of information.

Memory Array

Now back to the address bus. The number of conductors or wires assigned to the address bus will determine the maximum amount of memory addressable by the CPU. Remember that computers count in BINARY. Each additional binary digit that is added doubles the number of possible combinations. Early data buses used 8 conductors and therefore 256 combinations could be used. When referring to the address bus, we are interested in the maximum amount of RAM that it can address. Early computers used 20 address conductors and could address up to 1,048,576 combinations (bytes) of memory locations. That meant that under no circumstance could you run a program that needed more than one megabyte of data.

You will need to understand that when we talk about memory, you must keep in mind two numbers - the actual number and the rounded off number. For example, a 1 Kilobyte (1 K) of addressable memory - the base value used in computing is 210 (2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2) or 1024. We call this one Kilobyte (since it's about a thousand). A Megabyte is 1000 x 1000 or 1K x 1K or more precisely, 1024 x 1024 or 1,048,576 bytes.

Don’t confuse the rounded number with the actual number. Be sure that when you speak (or are asked a question) you know which term you are using.

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The combination of ones and zeros on the address bus tells the memory chips which byte of memory to address. In the case of a 32-bit address bus, the possible combinations of all on or all off, or any combination therefore is 4,294,967,296 (2 to the 32nd power).

The following tables show the affect on maximum memory when increasing the number of address wires.

Maximum Memory

Number of Address Wires

Maximum Addressable Memory

20 1,048,576 or 1 MB

24 16,777,216 or 16 MB

32 4,294,967,296 or 4GB

The following figure graphically shows an external data bus and CPU. Notice that the address bus is connected to the memory chip that in turn tells the RAM which data (one row in the array) to place on the data bus.

CPU and RAM

You may wonder how the memory chip knows when to read or write to the data bus. The answer is simple, the address bus actually uses more than the required numbers of wires to define the address. There are additional wires that the CPU uses to tell the memory when to read (take data off the data bus) or write (put data on the data bus). They are part of the bus, but not used to determine the maximum addressable memory.

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Motherboard Compatibility

One last word on motherboards - compatibility. Motherboards are like automobiles; many manufactures often use the same parts (or at least the parts perform the same functions), but they are not interchangeable. You must know the specifics of your car and the parts required before making a purchase. Therefore, when you face this issue of upgrading or replacing a motherboard you will have to consider many things. While highly unlikely, if you are replacing your motherboard with an identical motherboard, you will encounter few problems. If not, consider the following:

• The physical size of the board.

• Location of the mounting screws.

• Size and speed of the processor.

• Number and type of expansion slots – determines if your other equipment will connect.

• Type and amount of memory.

Processor Technology

If you review the history of the computer from the ancient Chinese Abacus to today’s high-speed marvels, you will note that technology progressed in jumps usually centered on some technological breakthrough. With each new technological breakthrough the computer was, and continues to be, elevated to new heights. Most of these developments are based on the progression of the CPU (Central Processing Unit).

For most people, to identify the CPU (Central Processing Unit) as the “brain” of their computer is sufficient. However, for the Computer Professional, this definition is just too simple. The CPU is a complicated, highly integrated chip that performs many different, simultaneous functions. To understand the principles of how the microprocessor works is to understand the computer.

Fortunately, the Computer Professional is not required to design a microprocessor, only understand how they work. Microprocessors can be viewed as a little black box. Inside this box is a wealth of information and the genius to resolve nearly any problem. We saw in the previous section that the CPU uses the external data bus and the address bus to communicate with devices in the computer and memory. Now we need to look at some additional components that support the CPU.

The Main Processor

The CPU (Central Processing Unit) is the part of a computer where arithmetic and logical operations are performed and instructions are decoded and executed. The CPU controls the operation of the computer. A microprocessor is an integrated circuit that contains a complete CPU on a single chip. The following figure shows a close-up of a CPU and other chips on a motherboard.

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CPU

Although it is not necessary to know exactly what goes on inside the processor. Here are a few terms that will be encountered by Computer Professionals:

Transistors

A transistor is a small electronic device that allows a small current to control a larger current. They are used as amplifiers and as switches in electronic circuits. Transistors replaced the old vacuum tubes used with the very first computers. Without the transistor, computers would not be what they are today. Microprocessors are made of thousands of transistors all incorporated into one chip. Today’s Pentium chips have millions of transistors.

Integrated Circuit

An integrated circuit is an electronic device consisting of many miniature transistors and other circuit elements (resistors, capacitors, etc.). The first integrated circuits were developed in the late 1950s. As manufacturing technologies have improved, so have integrated circuits. The ability to make circuits smaller and smaller allows more devices to be placed on the same chip.

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Microprocessors

A microprocessor is an integrated circuit containing the entire CPU of a computer, all on one chip. Only memory and input-output devices need to be added. The first microprocessor, (the Intel 8080) sold in 1973 for $400.00. It now sells for about $1.00.

Registers

Once data has been placed on the data bus, the CPU needs a method of temporarily storing or manipulating the data. Inside the CPU are temporary memory storage areas called “registers.” Each register is a microscopic circuit called a TTL (Transistor-Transistor Logic). The TTL is made of a row of 16 “flip flop” circuits (16 bits long). Each of these circuits can be held in one of two states (ON or OFF). If they are holding a charge, they are "ON.” If they are not holding a charge, they are "OFF.” The CPU uses these registers like workstations for manipulation of the data.

Clock

Timing is everything. Without some means of timing and synchronization, there would be chaos. Just as a conductor or metronome sets the pace for an orchestra, clocks are used to set the pace for all activities inside the computer. Each time a clock “ticks” it sends a pulse. One pulse is considered a clock cycle. All the switching activity in the computer occurs while the clock is sending a pulse. Between the pulses, the electronic devices in the computer are allowed to stabilize and execute all internal commands. Usually, a motherboard will have two clocks. One is used to control the speed of the CPU while the other is used to control the speed of the external data bus. This is done so that a single motherboard can accommodate several different CPU speeds while maintaining a constant speed for all the devices on the external data bus. The following figure graphically shows an external data bus with a CPU and two devices. Notice the crystal or clock is attached to the CPU to set the timing.

CPU with Clock

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The main selling point for computers today is the system clock rate - measured in Megahertz (MHz) or millions of cycles per second. If a command requires 2 cycles to complete (minimum time required to execute a command), then a 1 MHz computer can execute 500,000 commands in one second. The process of adding two numbers together would take about four commands (8 clock cycles) or 125,000 calculations per second. Today’s computers, running at 350 MHz, could then do about 44 million simple calculations per second.

Clock speed is determined by the CPU manufacturer and is the fastest speed at which the CPU can operate. The Intel 8088 processor had a clock speed of 4.77 MHz. Processors today have clock speeds up to and over 2.0 GHz and still climbing!

One method of increasing the processor speed is to increase the speed of the clock on the motherboard. This is called clock doubling or tripling. Often a motherboard will be designed for several versions of CPU, thus you can upgrade to a faster chip. When you upgrade, part of the installation will include the changing of a jumper that will in turn increase the clock speed. For example, upgrading a 33 MHz chip to a 66MHz chip would require that the clock be doubled.

Remember that this speed is the CPU’s MAXIMUM speed. If you place too many clock cycles on a CPU, it will overheat and stop working. The term used when running a CPU at speeds that are faster than recommended is overclocking. While this can be done, it is not recommended.

One of the unique properties of a crystal is that when excited by electricity, they will vibrate at a precise frequency. Crystals have been used to provide timing for many years. The very first radios were called crystal sets because they used crystals to tune the frequency. When you purchase a good watch, a crystal usually times it. Depending on the type, size, and cut of the crystal, various frequencies can be generated. For these reasons, crystals are the choice for timing on electronic equipment like computers. Look for a silver part, usually with a label, indicating the crystal speed.

Note: Do not confuse this clock with the one that keeps time. They are two entirely different devices.

Processor Voltages

The operating voltage in any electronic piece of equipment represents the power of the device. The higher the voltage, the more power it has, and the more power it consumes. Unfortunately, the by-product of power is heat. As CPUs get faster and more powerful, they produce more heat. Heat is destructive and causes failure of the CPU. Thus, cooling is an important part of the design for both the CPU and the motherboard. Fortunately for us, engineers have been able to design processors so that they can operate on less and less voltage. Three advantages come with the reduction in CPU voltages.

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• Reduction in overall power consumption.

• With less power comes less heat.

• A processor running cooler on less power can be made to run faster.

Knowing the processor voltage is an important part of servicing, replacing, or upgrading a CPU. If you install a new CPU and the voltage is too high, it will damage the chip. If the voltage is too low, the chip either won’t function at all or will function poorly. Oddly enough, the newer higher speed processors often require less voltage so if you don’t set the correct voltage, you will damage the new processor.

Changing the voltage settings can be as easy as setting a jumper on the motherboard or changing the voltage regulator. Many CPU upgrades will come with the correct voltage regulator and instructions for installation. Always check the motherboard and CPU specifications before you install.

In the next section, we will look at various configurations for CPUs and the socketsin that they are installed. On some of these, setting the correct voltage is important to prevent damage to the CPU. For example, while setting the correct voltage when installing a processor into socket 7 is important, it is less of a problem with socket 8 or the new SEC slot 1 and 2. These sockets and slots have pins that identify the correct voltage to the motherboard so that it can automatically make the adjustments. The best advice is to be aware of the voltages and check before you install. Typical voltages run between 3 and 5 volts DC.

Replacing a processor will depend on the type of socket employed by the motherboard manufacturer and the requirements of the processor manufacturer.

Processor Mounts

Processor chips are installed just like any other IC (integrated chips). While most chips are permanently soldered to the circuit board, those that may require changing are installed on a socket. A socket is a small plastic “stand” with holes for the pins of the chips. The socket is soldered into the circuit board and the chip is inserted into the socket. Each chip contains an array of pins that must be inserted into the correct socket. The number one pin is always marked on both the socket and the chip to insure correct alignment. Since CPUs often contain hundreds of pins, a method to provide simple replacement without damage to the pins was required. To help keep things simple, you will encounter only three different socket types for processors. The design of each is based on the difficulty required to insert the CPU into the socket. The three socket types are:

• Low Insertion Force (LIF)

• Zero Insertion Force (ZIF)

• Single Edge Connect (SEC)

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Removing an old CPU from LIF socket is a challenge that requires patience and persistence. While there are some special tools for removing these chips, most technicians use a pair of pliers and a small flathead screwdriver. The worst technique that you can use is to attempt this while the motherboard is still in the case. While it can be done, only the most skilled and experienced will be successful. You should remove the motherboard from the case before attempting to remove the CPU. With the motherboard out, you will have plenty of access, be able to carefully, and gently pry the chip out of its socket. You must be careful that it comes straight up out of the socket, do not pull it out at an angle! If using a screwdriver, apply it to each of the four corners one at a time and a little at a time until it is free.

When replacing the chip, you must be sure the number 1 pin goes into the number 1 pinhole. One corner of the chip will either have a dot or have the corner shaved off. This indicates the number one pin. The socket likewise will have a number or notch on one corner to indicate the number 1 position. Some will have a pin in one corner missing. To insert the chip, align the pins and press firmly until it goes in all the way. If it doesn’t “feel right” then something is wrong. Remove it and check the pins to be sure that none are bent, and try again. Remember that despite the name, it takes quite a bit of force to insert the chip. Be careful not to damage the board while inserting the chip.

Today, most motherboard manufacturers use the ZIF (Zero Insertion Force) socket. No force is needed because it has a lever that is used to disengage the contacts to the pins. When a chip is installed, the lever is opened, the chip dropped in and the lever lowered to engage the pins. The figure below shows how easy it is to remove a CPU from a ZIF socket. The most important thing to remember when installing a CPU into a ZIF socket is to make sure that the chip is designed to match the socket. Socket types are numbered will be between 1 and 8. They are clearly marked on the socket and in the motherboard documentation. To install the chip, simply open the retaining arm, drop the chip in, and lock the arm in place. Don’t forget to check for pin alignment and if you have to force the chip, then something is wrong.

Removing a CPU from a ZIF Socket

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Note: Socket 7 or the ZIF socket is used by many processors such as late Pentiums (i.e. – Pentium MMX), AMD (i.e. – AMD K6) and Cyrix processors.

SECC (Single Edge Contact Cartridge)

With development of the Pentium II processors, Intel went away from using sockets for installing processors in favor of the new slot. Just like the slots for mounting expansion cards, the Pentium II, and Pentium III, processors are mounted on their own circuit board that in turn is installed in a special slot. Currently there are two slot types (Slot 1 and Slot 2) for Pentium processors and one for AMD processors (Slot A).

The SECC2 (Single Edge Contact Cartridge 2) is used for the Pentium III and the SEPP (Single Edge Processor Package) is used for the Celeron.

Summary of Socket Types

Socket Type

Maximum Processors Supported Pin Count

Voltage

1 5x86 – 133 with 3.3v adapter 169 5v

2 5x86 – 133 with 3.3v adapter 238 5v

3 5x86 – 133 237 5v/3.3v

4 Pentium overdrive 133 273 5v

5 Pentium MMX 233 or AMD K6 with 2.8v adapter

320 3.3v

6 486 Processors 235 3.3v

7 Pentium, Pentium MMX 233, AMD K5 and K6

321 Uses a voltage regulator

8 Pentium Pro 387 3.1v or 3.3v

370 Celeron, Celeron II, and Pentium III

370 1.05v – 2.1v

423 Pentium 4 (older standard) 423 1.0v – 1.85v

478 Pentium 4 (newer standard) 478 1.0v – 2.0v

A (462) AMD K7 (Athlon), Duron, and XP 462 1.3v – 2.05v

Super7 AMD

Pac418 Itanium 418

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Summary of Slot Types

Slot Type

Maximum Processors Supported Pin Count

Voltage

Slot 1 Pentium II 333 MHz (66 MHz bus), Pentium II 450 MHz (100

MHz bus) & Celeron

242 2.8-3.3v

Slot 2 Pentium II Xeon (100 MHz bus) 330 1.3v – 3.3v

Slot A K7 (Athlon) N/A

Support for the Main Processor

The development of the microprocessor and micro-circuitry has been on the leading edge of the development of computers. One interesting aspect of this technology is the chip itself. If you look inside any electronic equipment, and more specifically on any circuit board, you will find it populated with many small, usually rectangular, “chips.” Each of these will have a multitude of fingers or wires that are used to connect the internal electronic circuitry to the circuit board. In fact, the electronic circuitry is only a small part of the chip. The majority of the chip is the package that allows it to be mounted on a circuit board. To help resolve the problems associated with circuit board design, the chips were designed to meet certain physical dimensions that include the chip, the number of connectors and the location of the connectors. Thus, the development of standard chip packages and a decrease in the cost of manufacturing for both the chip designers and the circuit board designers. Now, anyone manufacturing a circuit board could design to specific chip packages. The packaging has no bearing on the circuitry or performance of the chip inside. The following is a summary of the most popular chip packaging, starting with the earliest design. You will notice that often, several different processors were designed in the same package. Using this technique allows for easy upgrading (within the technical limits of the processor). For example, a Pentium 75 can be upgraded to a Pentium 166 because they both use the same chip package.

The following defines the most common types of chips packages found in computers. They are listed in their order of development and complexity.

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DIPP

The old standard for chip design is the DIPP or dual in-line pin package. It is also called a DIP (dual in-line pin) for short. You will see these chips on almost any circuit board. They have many functions including memory chips, microprocessors and just about anything else. DIPs are the black rectangular chips with two rows of pins one on each of the long side of the package. They will always have an even number of pins, but the pin count can be as low as 4 and as high as 40. It is always important to note the location of pin number one. This will insure proper installation. Pin number one is the first pin on the left of the end with the orientation notch when viewed from the top (the orientation notch is pointing away from you). When it comes to microprocessors for computers, you will find these in the older 8086, 8088 and 80286 models.

DIPP

PGA

With the implementation of the 32-bit bus, the pin count requirements exceeded the standards for the DIPP packages. It would also be impractical to use long narrow chips with hundred of pins. These packages require between 112 and 168 pins. The 64-bit Pentium chips would soon require up to 300 pins. To resolve this issue designers developed the PGA or Pin Grid Array. As its name implies, it is an array of pins instead of rows. It is actually a square chip with several rows of pins evenly spaced around the parameter of the chip to form the array. The center is void of pins. The number one pin is usually marked by a dot or by shaving the corner of the chip.

When working with PGA chips, be aware that there are several types of sockets to accommodate them. The two important differences are the number of pins and whether or not they are regular or ZIF. A regular socket requires that the chip be inserted the same as their predecessor the DIPP. A ZIF, or Zero Insertion Force socket will have a lever mechanism that will open the socket and allow the chip to be inserted with no force. Then the lever is locked into position to make an electrical contact and hold the chip in place.

PGA chips are common for 80286, 80386, 80486 and Pentium microprocessors.

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PGA

LCC

If you have ever had to install any chips, you will know the pins are a problem. Trying to align 40 plus pins into 40 plus small holes takes good eyesight as well as a lot of luck. Often one pin would get bent and the chip would fail. Even more of a problem is when you remove the chip and bend the pins. Now while trying to straighten them, one of them breaks off. To resolve these problems, some creative designers made the LCC or Leadless Chip Carrier. Along with these came the companion leadless chips. These are the same chips but instead of having pins, they have contact pads around their perimeter. These pads are made to contact special contacts in the socket so that when the socket is properly engaged and locked down with its retainer, the chip maintains good electrical contact.

PLCC

Typical PGA and LCC chips were manufactured with ceramic materials. This gave them the strength to prevent damage. An alternate form of this chip is the PLCC or Plastic Leadless Chip Carrier. While it does not have the strength of the ceramic chips, it does have some advantages. First, it is lower in cost. Another advantage is its ability to use the new surface mount technology. This technology allows manufactures to solder chips directly on the surface of a circuit board. This provides for a more automated manufacturing process and reduction of cost. The down side is that once soldered, they are not easily replaced.

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PLCC

PQFP

A development that came out of the LCC and PLCC designs is the PQFP or Plastic Quad Flat Pack. This chip combined some of the qualities of its predecessors and filled a unique market place. With their low profile, lightweight, plastic case and the ability to be soldered onto a circuit board, they are ideally suited for the laptop market.

SECC (Single Edge Contact Cartridge)

With the evolution of the Pentium II and III came a new method of attaching the CPU to the motherboard. The processor is part of a circuit board or card, is installed in a slot, and is called a Single Edge Connector.

History of Processors

Microprocessors have developed from the first 8088 to today’s high-speed Pentiums. Each new processor has brought with it new technology. Four basic elements have customarily been used to measure the performance of each new chip design.

• Speed - the maximum number of clock cycles measured in MHz (megahertz). Higher speed means more commands executed in less time.

• External Data Bus - As data bus size increases, so does the amount and complexity of code (information) that can be transferred between all devices in the computer.

• Address Bus - The size of the address bus determines the maximum amount of memory addressable by the CPU.

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• Internal Cache - Internal cache is high-speed memory built into the processor. This is a place to store frequently used data and avoid using slower devices (speed is relative in computers) such as RAM and hard drives. It is built into the processor and has a dramatic effect on speed.

The following is a summary of the development of processors from the early 8088 to today’s Pentium IV. Recognizing that there are several manufacturers of CPUs such as Intel, AMD and Cyrix, this comparison of microprocessors will be based on the Intel family. While a detailed study of microprocessors is far beyond the scope of this training, as a computer professional, you may want to purchase one of the many books devoted to this topic.

In the Beginning

In 1978, Intel introduced their first 16-bit microprocessor known as the 8086. The processor had 16-bit registers, a 16-bit external data bus and a 20-bit address bus to allow it to access 1 MB of memory. When IBM entered the computer business, the 8086 was too advanced (and expensive) to meet their requirements of most electronic equipment of the day. To meet the needs of IBM, Intel introduced the 8088. This is the same as the 8086, but with an 8-bit external data bus. This modification meant that 8-bit components (more common at the time) could be used for the construction of computers and 8-bit applications written for the computers predecessors could be converted for computer use.

8088

Manufacturer Intel

Speed (MHz) 4.77 to 10

Data Bus - Bits 8-Bit

Address Bus -Bits 20-Bit

Cache None

8086

Manufacturer Intel

Speed (MHz) 4.77 to 10

Data Bus – Bits 16-Bit

Address Bus -Bits 20-Bit

Cache None

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The early 8088 processors ran at 4.77 MHz while later versions ran at 8 MHz. The original IBM Computers used the Intel 8088 microprocessor. The processors came as a 40-pin DIP (Dual In-line Package) containing approximately 29,000 transistors.

The 8088 and 8086 are compatible - they can run exactly the same software. The benefit of using an 8086 is the 16-bit external data bus. This makes an 8086-based computer execute the same software faster than an 8088 computer with the same clock speed.

Features of the 8088/8086:

• 16 K of memory.

• Cassette tape recorder - for program and data storage.

• Non-graphical monochrome monitor.

THIS FAMILY OF CHIPS IS CONSIDERED THE BENCHMARK MICROPROCESSOR.

The Mainstays

These next three processors began the rapid expansion of computer processors, as we know them. They literally broke the mold. By overcoming the limits of the 8088 and 8086, they opened the door for color and graphics. Each one is a step up from its predecessor.

80286

In 1981, Intel released the first 80286. In 1984, IBM released the AT-Computer, which used the Intel 80286 processor. The AT was the first microcomputer to be cloned by large numbers of other manufacturers. The main advantage of the AT was that it could run the same applications as an XT but faster. Intel manufactured the 286 microprocessor that operated at 12 MHz. Intel licensed the specifications of the 286 to other IC (Integrated Chip) manufacturers, notably Harris and AMD, who made versions of the 286 that could run at up to 20 MHz.

80286

Manufacturer Intel

Speed (MHz) 8 to 20

Data Bus - Bits 16-Bit

Address Bus -Bits 24-Bit

Cache None

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The use of a 24-bit address path allowed the 286 to access up to 16 MB of memory. The processor came as either a DIPP or a PLCC. The PLCC can be recognized by the arrangement of thin legs around its perimeter.

Features of the 80286:

• Ability to use Virtual Memory

• Ability to Operate in two Modes (Real and Protected)

• Address 16 MB Memory

• Clock Speeds up to 20 MHz

• Reduced Command Set (fewer program commands to do more work)

• Multitasking Abilities

Virtual Memory

Virtual Memory can be described as hard disk space, which can be used as additional memory for holding data not immediately required by the processor. This technique allowed the 286 to address up to 1 GB of memory (16 MB of actual memory and 984 MB of virtual memory). This feature was used by the new generation of operating systems such as Windows and OS/2.

Real Mode vs. Protected Mode

With the introduction of this chip came two new terms, real mode and protected mode. These are important concepts that you will hear repeatedly.

• Real Mode - the 286 emulates the 8086 processor and consequently can only address the first 1 MB of memory. This mode ensures the AT machines are backward compatible with software written for the earlier Computers.

• Protected Mode - this mode allows the 286 to access all available actual and virtual memory. In protected mode, different parts of memory are allocated to different programs. The memory is “protected” in the sense that a program can only write to the memory allocated to it. In addition, this mode allows for multi-tasking programs.

Limitations

When the 80286 was first released, it was too powerful for its time. Only special applications were able to take advantage of the performance improvement of Protected Mode. In order to switch between Protected Mode and Real Mode, the computer had to be re-booted (turned OFF and then back ON).

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80386

In 1985, Intel introduced the 80386. This processor had two forms:

80386DX - this was a full 32-bit processor with a 32-bit external data bus, 32-bit registers and a 32-bit address bus (enabling 4 GB of memory to be accessed). The processor was capable of addressing 64 TB (tera bytes - a trillion bytes) of total (actual and virtual) memory. The 80386DX can easily be identified with its square shape, distinct inscription and its blue tint.

80386 DX

Manufacturer Intel

Speed (MHz) 16 to 33

Data Bus - Bits 32-Bit

Address Bus -Bits 32-Bit

Cache None

80386SX - this processor was similar to the DX except that it had a 16-bit external data bus and 24-bit address bus (it could only address 16 MB of memory). The 16-bit configuration allowed easy upgrading from existing 16-bit motherboards, therefore introducing the next generation of computers.

80386SX

Manufacturer Intel

Speed (MHz) 16 to 25

Data Bus - Bits 16-Bit

Address Bus -Bits 24-Bit

Cache None

The 80386 chip was originally offered with speeds of 12 or 16 MHz. Intel produced faster 25 and 33 MHz versions, while AMD manufactured a 40 MHz variant. The 386 provided both the real and protected modes available in the 286. In addition, the 386 had a third mode called “virtual real mode” which allowed DOS programs to be multi-tasked. This processor mode allows independent DOS sessions (called “virtual machines”) to co-exist on the same system.

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The 386 came in either a PLCC package or a PGA package. The 386 had the equivalent of about 250,000 transistors.

Features of the 80386:

• 32-bit address bus allows up to 4G of addressable memory;

• Allows the use of GUI (graphical user interface).

80486

In 1989, the 80486 line of processors was released. The 486 processor is the equivalent of an upgraded 386DX. Inside the 486 is a faster and more efficient 386 processor, an 80387 numeric coprocessor, a cache controller and an internal 8K cache. This was the first truly integrated chip.

80486

Manufacturer Intel

Speed (MHz) 25 to 100

Data Bus - Bits 32-Bit

Address Bus -Bits 32-Bit

Cache 8 KB

The 486 ran at clock speeds up to 133 MHz. Improvements in its architecture allowed the execution of a single instruction in two clock cycles rather than the four cycles of the 386. The 486 was manufactured at higher tolerances than the 386 (circuit lines and spaces down to 0.8 microns). This meant that more transistors (1.25 million) could be packaged into the chip and both a numeric coprocessor and on-board cache could be included in one unit.

Intel 486 processors could be “clock-doubled” or “clock-tripled.” These were called the 486DX2 and 486DX4 respectively. These processors were either 25 or 33 MHz versions that have been altered to run internally at double or triple their external speed. For example, the DX4 version of the 486, 33 MHz processor runs at 33 MHz externally, but internally at 100 MHz (3 x 33.3 MHz). This difference in speed means that internal operations like numeric calculations, or moving data from one register to another, occur at 100 MHz, while external operations like loading data from memory takes place at 33 MHz. Slower external clock speeds (25 or 33 MHz) allowed existing motherboard and memory designs to be used, which meant that existing 486 systems could be readily upgraded simply by the replacement of the processor. The DX4 processor was provided with 16K of on-board cache to improve performance.

The 486SX is a version of the 486 with the math co-processor disabled - it is cheaper than the full “DX” version of the 486. Math co-processors were traditionally add-on processors that increased the mathematical power of a CPU. Most motherboards came

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with two processor sockets, one usually empty. The co-processor could be added-on later to increase the power of the computer. While the DX incorporated the math coprocessor, the SX was a fallback to the old ways. Intel claims that only 30% of users need a numeric coprocessor. It is still a full 32-bit CPU.

Originally designed for the laptops, the 486SL ran at lower voltage (3.3 volts instead of 5 volts). The small powerful machines also included System Management Mode (SMM), which can dim the LCD screen and power down the hard drive. These features extended the life of the battery.

The DX2 50MHz based machines should not be confused with machines designed around the 50MHz 486DX processor. This runs internally and externally at 50MHz and it is targeted at input/output intensive applications such as network operating systems and CAD (Computer Aided Design).

Features of the 80486:

• Improved instruction set.

• Math Co-processor is included in the chip.

• Internal cache memory.

Today’s Standard

The next major jump in processor technology brought us to what is today the industry standard. Let’s now look at the development of the Pentium Processors.

Pentium

1993 was a big year as Intel introduced the Pentium. What made this chip big news was that it was not just a new and improved processor as all previous introductions; it was a true technological advancement. The most important features were the 32-bit address bus and 64-bit data bus. These new chips required the addition of a heat sink and cooling fan as standard equipment. If the cooling fan were to fail, they would literally burn up (or melt down) from the heat generation.

Pentium

Manufacturer Intel

Speed (MHz) 60 to 200

Data Bus - Bits 64-Bits

Address Bus -Bits 32-Bits

Cache 2 each 8 KB caches (one for commands and one for data)

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Along with this new chip came many new (but now common) terms:

Pipelining - combining several processor steps into one clock cycle therefore increasing the speed of processing.

Dual pipeline – The availability of a 64-bit data bus allows it to be split, thus providing two 32-bit data buses. With two data buses, the chip could process two separate lines of code simultaneously.

Quad Word – A 64-bit data bus can handle four words at the same time (4 x 8).

Superscalar – A processor architecture that allows multiple instructions to be executed at the same time. This means that the Pentium has two instruction pipelines - called U and V. The U pipeline can execute the full range of Pentium instructions while the V pipeline can execute a limited number when required.

Multi-threading - When possible, the Pentium processor breaks up a program into discrete tasks that are then shared between the pipelines thus allowing the Pentium to execute two simple instructions simultaneously. Software needs to be specifically written to take advantage of this innovative feature - it has been labeled.

Branch Target Buffer – The Pentium processor includes a Branch Target Buffer (BTB) that is used for a technique called Branch Prediction. The BTB tries to anticipate when a program will branch and will store a few lines of code from each branch so that when the code reaches the branch it can retrieve the next set of instructions faster. This process allows the Pentium to keep both pipelines running at full speed.

In the early days of Pentium, Intel had problems manufacturing a reliable 66 MHz processor. However, by underclocking the speed to 60 MHz the processors became stable. Therefore, Intel marketed the their first chip as the P60.

The manufacturing problems that led to the speed reduction were centered on the technology to produce the small circuitry required for this chip. Therefore, Intel continued to use the 0.8-micron, (one thousandth of a millimeter) manufacturing process (used with the 486), to fit the 3.1 million transistors in the Pentium chip.

Note: The 0.8 manufacturing process means that 0.8 microns is the smallest etching (size of a line or a space between two lines), which can be made on a chip. Approximately 16 thousand lines and spaces to 1 inch.

With the technology to overcome the 0.8-micron limit in 1994, Intel released their next Pentium version. These later processors were made using a 0.6 micron manufacturing process (Approximately 21 thousand lines and spaces to 1 inch) and, as a result, they required considerably less power despite an additional 0.2 million transistors. Intel was able to change the power supply from 5v to 3.3v (the DX4 also had a reduced power supply) and reduced the amount of heat produced by nearly one half. The P90 and P100

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processors were released at this time. These processors ran internally at 1 ½ times the external speed (60 or 66 MHz). At this time, the fastest system boards available ran at 66 MHz. A P75 processor was also released for use in lower specification machines and laptops.

Released in 1995, the P75 used a 0.35-micron process (Approximately 36 thousand lines and spaces to 1 inch). The P120, P133, P150, P166 and P200 use internal clock speeds that have been increased by factors of 2 and 2 ½.

Another feature that has now been incorporated into all new chips is the addition of on-board cache. Cache, as it will be explained in detail in the next chapter, is special fast (and expensive) memory. Pentiums have two 8K caches, one for data and one for program code, compared with the single 8K cache on the 486 (16K on the DX4). The cache uses branch prediction to improve its ability to guess what data or program code will be required next by the processor.

Until recently, all the Intel processors have been based on CISC architecture (Complex Instruction Set Computer). While high-powered machines have been using RISC-based processors (Reduced Instruction Set Computers) since the mid 1980’s. These processors use a much smaller and simpler set of instructions to control the processor. The use of simpler/shorter instructions greatly enhances the speed of the processor.

Pentium Pro

Intel's successor to the Pentium processor, the Pentium Pro, was a departure from merely increasing speed and was available in September 1995. The Pentium Pro has an internal RISC architecture with a CISC-RISC translator, 3-way superscalar execution and Dynamic Execution. While compatible with all of the previous software for the Intel line, the Pentium Pro is designed to run 32-bit software. It also had a change in the pin structure and is not compatible with previous Pentiums.

The Pentium Pro adopted a 2.46” x 2.66” 387-pin PGA configuration to house a Pentium Pro processor core and an on-board cache. While on the same PGA device, the two components are not integrated into the same IC. A gold-plated copper/tungsten heat spreader covers the unit.

The Pentium Pro was made as a two-chip assembly: the first chip is the CPU and 16 kilobyte first level cache (5.5 million transistors) and the other is a 256 (or 512) kilobyte second level cache (15 million transistors). Running at a clock speed of 133 MHz, a Pentium Pro will perform at approximately twice the speed of a 100 MHz Pentium.

Dynamic Execution is a combination of three techniques that rapidly increase processing efficiency. Before instructions are processed, an analysis of the data flow is made to discover the optimal sequence for execution. Then, because it can look up to thirty instructions ahead into a program and predict where the next branch or group of instructions can be found in memory, it can process one instruction without waiting for another to be completed. Up to five instructions can be processed speculatively and the

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results stored until they are needed. This whole process is similar to a chess player predicting his opponent's moves and working out the outcome of each of his options. By using a technique known as “Data Flow Analysis,” the Pentium Pro can determine dependencies between data items so that they can be processed as soon as their inputs are available, irrespective of the program’s order.

Pentium II

With the development of the Pentium II processor, the traditional chip and socket design went by the wayside. These chips are mounted on their own circuit board and housed in the new SEC cartridge. This cartridge uses a special retention mechanism that is built into the system board to hold it in place. The cartridge also has a special fan heat sink module and fan. This also requires special supports to hold it in place. A special power connector located on the system board provides power to the fan, or one of the systems optional power connectors is used. So, the SEC cartridge houses the CPU, the L2 cache, heat sink and fan.

These processors are based on 0.35-micron technology for speeds of up to 300 MHz and 0.25-micron technology for speeds in excess of 400 MHz. The core chip has 7.5 million transistors. Another advance of these higher speed processors is that the voltage requirements have also decreased from 2.8v 300 MHz or less to 2.0v at 400 MHz or more. Pentium II processors have better performance and capacitor technology than Pentium I processors.

Celeron

The Intel Celeron processor is used in both workstations and appliance servers. Speeds presently available for the Intel Celeron processor range from 500 MHz to 700 MHz. The Intel Celeron processor includes a 128 KB L2 cache and it implements the P6 system bus, which runs at 66 MHz. MMX capabilities are included in the Celeron, which provide multimedia functions. Streaming SIMD extensions are also a part of the Celeron, which provides advanced imaging, speech recognition and streaming audio and video. The Celeron functions best with applications with a low-priority that don't require much processor overhead.

Pentium MMX

The Intel Pentium with MMX (Multi-Media eXtension) technology has been specifically designed to enhance performance with today's data hungry applications. Available at both 166 and 200 MHz, it was introduced early in 1997 and was the first processor with MMX technology.

By doubling the size of data and code caches to 16K each, the Pentium with MMX technology runs non-MMX enhanced software at approximately 10-20% faster than the original Pentium processor at the same clock speed. To reap the full benefits of the new processor, “MMX enhanced” software must make use of the 57 new instructions. This unleashes the additional performance provided by MMX technology, enabling more colors, more realistic graphics, full screen, full motion video and other multimedia enhancements. In addition, performance increases of up to 60% can be achieved.

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MMX technology is based on Single Instruction Multiple Data (SIMD) techniques. This means that many processing elements perform the same operations on different data - a central controller broadcasts the instructions to all processing elements at the same time.

The use of branch prediction, as introduced on the Pentium Pro processor, has been improved. Dynamic branch prediction uses the Branch Target Buffer (BTB) to boost performance by predicting the most likely set of instructions to be executed.

One of the major advantages of the Pentium with MMX technology over the Pentium Pro is that it more easily handles 16-bit technology, making it more backward compatible than its predecessor. It will take a while for software developers to catch up with the developments for MMX technology and for the greatest improvements to be made. The new instruction sets were not designed to speed up existing software, but to pave the way for more efficient multimedia applications by providing specific instructions to deal with the kind of repetitive loops that are associated with pixel and audio-based data.

Pentium III

The next release of Pentium was the Pentium III. The Pentium III offers clock speeds of up to 800 MHz. The “Katmai New Instructions” provide 70 new computer instructions, which make it faster to run applications that can take advantage of them. These include 3-D, imaging, Internet streaming SIMB extensions, speech recognition and audio applications.

The Katmai New Instructions support floating-point units as well as Single Instruction Multiple Data instructions. This technology significantly speeds up processing of multi-media applications, which allows the viewer to see a much smoother presentation.

Pentium III Xeon

The Intel Pentium III Xeon can function at speeds of 866 Mhz or so, and are ideal for use in servers. The Xeon offers 256 KB of L2 cache and a system bus of either 100 Mhz or 133 Mhz. The Intel Pentium III Xeon is used for mid-range to high-end servers. If a server can support up to 32 processors via hardware and software, the Xeon is an excellent choice. The Xeon processor also includes a thermal sensor, which monitors the core temperature.

Pentium 4

Intel has introduced the Pentium 4 processor as the new generation of Pentium processors. It is touted as technology that was designed for the Internet and beyond. It is based on the all-new Intel NetBurst™ micro-architecture, and boasts 42 Million Transistors. Intel anticipates this processor to significantly improve performance in today’s multimedia environment, but in addition, expects the improvements to extend many years into the future. Some of the improved features are as follows:

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400 MHz System Bus

400 MHz data transfers are supplied through a physical signaling scheme of quad pumping data transfers over a 100 MHz clocked system bus. This technique along with a buffering scheme allows for the sustained data transfers of 400 MHz. This system offers a performance increase of about three times that of the Pentium III.

Advanced Dynamic Execution

Performance is improved using Advanced Dynamic Execution by providing a large window of instructions from which the execution units can choose. This avoids delays that are caused while dependencies are resolved. This window may have up to 126 instructions, whereas previous architectures have only 42.

Rapid Execution Engine

Through a combination of methods, the simple Arithmetic Logic Units (ALUs) within the processor run at twice that of the processor core. This means that certain instructions will execute with latency that is one half the duration of the core clock and provide higher throughput.

Advanced Transfer Cache

The Level 2 Advanced Transfer Cache is 256K in size and is capable of providing a data transfer rate of 44.8 GB/s. This is a great improvement over Pentium III’s 16 GB/s.

Hyper Pipelined Technology

The Hyper Pipelined technology of the NetBurst™ micro-architecture doubles the pipeline depth of the Pentium III architecture.

Execution Trace Cache

This innovative way to implement Level 1 instruction cache stores decoded x86 instructions, thereby removing the latency associated with the instruction decoder from the main execution loops. It also stores these instructions in the flow of program execution so that instructions that are branched over are never executed. This results in a better use of cache.

Streaming SIMD Extensions 2 (SSE2)

SIMD (Single Instruction/Multiple Data) technology came out with the Pentium MMX. With the Pentium 4, it has been enhanced and is known as SSE2. SSE2 provides 144 new instructions that deliver 128-bit SIMD integer arithmetic operation and 128-bit SIMD Double-Precision Floating Point. What this all means is that the Pentium 4 can deliver increased performance that accelerates the delivery of a broad range of applications including: video, speech, image, photo processing, 3-D, gaming, encryption, financial, engineering and scientific applications.

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The performance increases resulting from these technological advances makes the Pentium 4 ideal for use at home, office, or networking. It is ideally suited for today’s Internet usage, and was designed to include “headroom” for future technological advances. It is currently available in speeds of 1.8 GHz to 3.0 GHz.

Hyper-Threading

Some of the newer versions of the Pentium 4 processor possess the ability to be utilized as if they were two logical processors. By using additional registers, instruction streams can be overlapped for a significant gain in performance. Even though this can be used with applications that take advantage of hyper-threading, nothing compares with actually having multiple processors.

Pentium 4

Intel Itanium

The Intel Itanium processor is used with high-end servers and it uses a 64-bit design that works with the standard 32-bit architecture. Most NOS vendors are working on support for this type of processor.

Pentium Processor Number of Transistors

Pentium 3.1 – 3.3 million

Pentium MMX 4.5 million

Pentium Pro 5.5 – 6.2 million

Pentium II 7.5 million

Pentium III 9.5 – 28 million

Pentium 4 42 million

Itanium 120 million

Itanium 2 410 million

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Co-Processors

During the early development of computers, (pre-Pentium) many motherboards had sockets for two processors - the CPU and the optional Math Co-Processor. This design achieved two goals. First, it kept the initial cost (the advertised cost) of a personal computer low and affordable. Second, most people and the software that they used, did not do a lot of math, so the main CPU could handle the work. On the other hand, if you were an engineer and used a computer to do math-heavy tasks without a math co-processor, you could expect poor performance. By purchasing an additional processor just to do the math, these poor performers could handle the task. In fact, many software programs, such as spreadsheets, came with a label “Math Co-Processor Required”. These co-processors were easy to identify as their names corresponded to that of the main processor. For example, if you had an 8088 processor, you purchased an 8087 math co-processor; an 8386, used an 80387, etc.

Beginning with some 80486s and the Pentium, the math co-processor became an integral part of the CPU. This is partially due to the advances in screen graphics and software that are more math intensive.

To install these processors, you simply placed them into the appropriate socket and moved a jumper to enable it. In some cases, you may have to make a BIOS change through the CMOS set-up.

Non-Intel Processors

A discussion of Pentium chips would not be complete without some mention of Intel’s competitors. Before the introduction of the Pentium, processor manufacturers were producing “clones” of the Intel processors. In fact, due to some contractual issues with IBM, Intel was required to provide the specifications for all 8088 based processors to their competitors. This way, IBM was sure that if Intel went out of business, they would still have resources for the chips they needed. We all know that Intel did not go out of business and with the release of Pentium technology which was not based on the 8088 architecture, Intel’s competitors were on their own. Therefore, they are currently designing their own processors with unique features:

• NextGen Nx586

• AMD AmSx86

• Cyrix 6x86

• IBM 6x86

These processors are all backward compatible with computer software. With this diversion of brand names, Intel’s competitors needed some method of comparing their products to Intel’s Pentium. The result of this is the “P-Rating.” This system rates a processor as equivalent to its nearest Pentium. One result of these competitors not relying on Intel specifications is that they began their own development programs. Today, there are many good and reliable processor alternatives to the higher priced Intel products.

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AMD processors are the most popular processors used today, short of Intel’s Pentium models. The following chart should give you a better idea of how certain AMD models stack up against their Pentium counterpart.

AMD Processor Pentium Equivalent

K6 Pentium II (266 MHz – 300 MHz)

K5 Pentium Class (116 – 166 MHz)

K4 Pentium Pro (150 – 200 MHz)

Athlon Pentium III (500 – 1.13 GHz)

Duron Pentium 4 (1.4 – 2 GHz)

Installing a CPU

When considering upgrading a CPU, there are many options to consider. Perhaps the most important consideration is the “value” of the upgrade. Will the suggested upgrade meet the operational requirements for that computer? The following table lists several possible scenarios for upgrading a CPU. The best recommendation is to check your motherboard documentation before making a decision or purchase. This will often tell you exactly what you can and cannot do.

VRM (Voltage Regulator Module)

Every microprocessor has specific voltage requirements for the core and I/O functions. When you upgrade a processor, you may need to install a VRM to make sure that the proper voltage is detected and facilitated.

Voltage Regulator Module

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Motherboard Upgrades

If you have: Then

80386 or older machine There is no real value in upgrading any of these machines. Very little software today will even run on them and they are restricted to DOS and Windows 3.1.

The best advice is that if it is working and doing a job then leave it alone. If it can’t do the job, get a new computer.

80486 There are still many good 80486 machines running. The best you could do is to add memory and check the documentation to see if you can get a faster processor.

Again, if it is not doing the job and you are going to have to upgrade any software such as the operating system, you are probably better off getting a new one.

You should consider replacing the motherboard with a Pentium or equivalent.

If you find that you also don’t have enough hard drive space and no CD-ROM, you might consider a new machine.

Early Pentium The best upgrade for one of these machines is lots of memory. They will still run most software and unless you are heavy into graphics, video and the Internet, you will still get some use before replacement.

Advanced Pentium The only reason to consider upgrading (except more memory) is because the current processor will not handle the job you need it to do. For most jobs, these computers will last several more years.

You may consider a new motherboard with a 100 MHz data bus. This will allow upgrades beyond 350 MHz.

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Replacing an existing CPU with an exact replacement is for the most part an easy task. Since all the specifications and configurations are the same, you will need only to pull out the old and insert the new. The amount of work to complete the task will depend on the type of CPU and what kind of socket it uses and whether or not you will need to configure the clock speed and voltage. Some of the earlier motherboards actually soldered the CPU in place. If you encounter one of these, you should probably get a new motherboard.

Keeping it Cool!

Nowadays, the interest in on-line gaming and overclocking has placed an even greater interest on cooling methods. There are various methods to keep your computer components cool and some are relatively new to the market. All of these methods have advantages and disadvantages, so both will be discussed.

Fans

Fans keep the internal temperature of the case down so internal components won’t suffer. Many cases will have the ability to use more than one or two fans. Some power supplies have multiple fans build in to keep things cool as well. Fans also come in a variety of sizes from 40 mm to 120 mm.

Fan

Heat Sinks

Heat sinks push the heat away from a CPU and are standard equipment used with processors. There are heat sinks that come with the processor when you by it or you can purchase specialized heat sinks.

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Heat Sink

Thermal Compound

This substance is used to transfer heat from a CPU to a heat sink. The compound bonds the two surfaces and facilitates better heat transference. Some heat sinks come with a small of amount of thermal compound already on them.

Liquid Cooling

Liquid cooling utilizes a radiator to keep your PC cool. Liquid is circulated through a heat sink affixed to the CPU. The liquid passes through the heat sink, the heat moves from the processor to the cooled liquid. The heated liquid moves to the radiator and the heat is placed in the ambient air outside of the chassis. The process is continued when the liquid is moved back to the heat sink.

Liquid cooled systems are much more efficient than conventional cooling methods like fans and good ventilation. The reduction in noise is also an big plus, since gamers want to hear what going on as much as they want to see what’s going on. Gamers aren’t the only one who benefit from the lack of noise with liquid cooling. People who integrate their computer with their home entertainment centers won’t want to hear a lot of racket while trying to watch DVDs or listen to the stereo.

Water-cooled Case

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Cooling to the Extreme – Liquid Nitrogen!

If fans, heat sinks, and water-cooling just aren’t enough, liquid nitrogen can be used to cool the motherboard in tandem with a non-conductive liquid. The motherboard will actually be submersed in the non-conductive liquid and the liquid nitrogen cools the non-conductive liquid through a pipe system. There is a case for the intercooler (that is submerged in liquid nitrogen), a case for the motherboard (submerged in non-conductive liquid) and a pump to connect them.

Diagram for a Liquid-Nitrogen Cooled Computer

There really isn’t a practical application of this technology for the home user, but some companies use systems with a similar concept. It is by far the most effective way to cool the internal components of a computer, but it is doubtful that you will find liquid nitrogen in your local computer store anytime soon.

Warning: working with liquid nitrogen is dangerous and should only be handled by professionals with experience dealing with dangerous chemicals!

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Summary

This chapter covers a lot of material on motherboards, processors and related components. The motherboard and the processor more than any other component define the limits of our computer. It is very important that when working with these two components that they work in harmony to reach the maximum performance of the system. While not a complete course in motherboards and processors, this chapter should give you enough information to understand their importance and how they relate to each other and how to go about identifying them and servicing them. The following summarizes the key points of this chapter:

• Understanding ROM/BIOS is key to keeping a computer up and running.

• CMOS setup defines the data a computer needs to communicate with its hardware (drives and so on).

• The CMOS battery maintains data when power is turned off.

• The motherboard defines the capabilities of a computer. It is the speed of the processor, address bus size, external data bus, and size of cache that determine the limits of the processor.

• Not all motherboards are the same. Some manufacturers have proprietary motherboards that can only be used in their own computers. They will also require proprietary parts for expansion. Generally, these motherboards are higher quality (and higher priced).

• BIOS chips are used to provide data to the CPU. This data tells the CPU how to operate specific devices.

• CMOS is a BIOS chip that can have its data updated. The CMOS setup program is used to make these changes.

• Some of the newer BIOS chips are updateable. These are called flash BIOS or Flash ROM.

• A device driver is a software solution for maintaining BIOS information for a specific device.

• POST is used to check a computer before it boots.

• POST errors are indicated by beeps before the video is checked and by text after the video check.

• The microprocessor is the centerpiece of today’s computers.

• The three key elements for measuring a CPUs performance are its speed, its address bus and its external data bus.

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• Be familiar with the types of processors available (Intel, AMD and Cirix).

• Replacing a CPU is a simple task. To be successful, you must check specifications for the socket, the voltage and speed of the processor to be sure that it is compatible with the motherboard.

• It is important for a computer technician to know the technological advances made by each successive generation of computers.

• Motherboards come in many sizes and shapes but there are generic boards that fit most clone computers.

• Chip sets are unique to each motherboard design and work with the CPU to compose a particular computer.

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KEYWORDS Exercise

Define each of the following keywords. Hint: There’s a glossary in the back of this book.

Keyword Definition

Address Bus

BIOS

Case

CPU

Chip Set

Clock

CMOS

DIPP

Electromagnetic Interference

External data bus

Firmware

Flash ROM

IC

Internal cache

LCC

LIF

Microprocessor

Motherboard

PGA

PLCC

POST

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Keyword Definition

PQFP

PROM

Protected Mode

Real Mode

Register

ROM

SEC

Socket

Transistor

ZIF

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Review Questions Chapter 4

1. What is the main function of the motherboard?

2. Name the typical chips found in a “chip set.”

3. What are ROM chips used for?

4. What makes CMOS so special?

5. How can a technician use the POST beep codes?

6. What information is contained in CMOS?

7. What is the language of the Computer?

8. What is an external data bus?

9. What is an integrated circuit (IC)?

10. What is a clock cycle?

11. All devices that require the handling of data are connected to what?

12. What improvement does a Pentium have over a 486?

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13. In a 386 chip, what is the difference between “SX” and “DX”?

14. What kind of a computer uses a Motorola 68040 chip?

14. In computer code language ________ means ON and ________ means OFF.

15. What is the function of the Address Bus?

16. Name the different chip packages.

17. Name the two basic types of CPU sockets.

18. If a customer brought you an old 486SX and wanted you to install a new processor, what would be your advice?

19. When upgrading a CPU, the three elements to check are _________, _______ and _____.

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Chapter 5 – Memory

The efficient operation of a computer is based on its ability to process data. CPUs require a method of storing data, both temporarily (RAM) and more permanently (ROM). RAM and ROM are extremely important concepts on the A+ exam. This chapter discusses the many technologies that exist to deal with these issues.

RAM & ROM

Memory can mean different things within a computer. ROM, or Read Only Memory, is made up of chips that hold the data that the computer uses every time it starts or boots. Since this information rarely changes, we don’t put much emphasis on it. The kind of memory that we are going to look at now is temporary memory. There are many names for this memory including working memory, on-line memory and volatile memory. Memory is included here in the section on storage because it is the first level of storing information in a computer. While it is only temporary, it is fast, and having enough memory to work with is vital to efficient operation of the system.

Early Memory

Programs are little more than a long list of binary code that is sent to the CPU for processing. Since each line of code is nothing more than a pattern of ones and zeros, any device that can store ones and zeroes in some detectable form will work as memory.

The very first computers, such as the one used in the 1890 census, used paper cards with holes punched in them. One card was used for each line of code. A stack of cards, when loaded in the right order and then run through a “card reader,” would load information into the “computer.”

Punch Card

This worked great for storing programs or inputting data into the computer, but what about the information generated by the CPU? To compute complicated equations, the CPU may have to generate hundreds or thousands of pieces of temporary information that is held and then returned to the CPU at the appropriate time. We needed some type of storage to which the CPU can write and read data. Modern computers use a combination of three kinds of memory; ROM, RAM, and Cache. Each is located on special chips and has its own advantages and disadvantages.

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Memory Types

Computer memory comes in two generic types. The most common type is the memory that we use every day to run our applications. The other type is permanent memory that stores data that the computer needs to run. Let’s take a closer look at these two types of memory.

ROM – Ready Only Memory

Read Only Memory - ROM is a special kind of memory, which contains code (data or a program) permanently installed by the manufacturer. By using ROM, information that is required to start and run the computer cannot be lost or changed. ROM is used extensively on computers that are designed for one purpose only (such as the one that controls the engine in your car). ROM in a computer is used for the BIOS chips (refer to the chapter on Motherboards for details on BIOS).

RAM - Random Access Memory

A CPU needs temporary storage space for programs and data. A hard drive, floppy drive or tape drive will hold the information, but the time required to read/write the information is too slow for today’s programs and CPUs. The device used to do this is RAM (Random Access Memory).

In the computer world, RAM arranges and stores data in byte wide (8-bit) pieces. RAM can be looked at in terms of an array of rows and columns. Each cell in this array can store only a “1” or a “0” (in this case, voltage or no voltage). Each cell can hold one “bit.” Each row in the array is eight bits across (to match the external data bus of the 8088) and holds one “byte” of information. Most computer memory is DRAM (Dynamic Random Access memory). There are many different varieties of RAM each with its own advantages and disadvantages.

RAM Array

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Everyday Memory

When discussing computers, one of the first things mentioned is how much RAM or memory does it have. The computer memory we are referring to is DRAM or Dynamic RAM. What makes DRAM so common is that it is cheap and fast.

One of the important attributes of DRAM and the reason it is called dynamic is that it requires constant refreshing, meaning that the memory registers are recharged. Most of us have experienced at one time or another a short power interruption while working on our computer and the resulting loss of data. That is because the CPU temporarily stores all the information in DRAM chips. Until that data is moved to a permanent storage media such as a disk drive, it is subject to loss. These chips require a constant voltage refresh in order to maintain the cells that contain ones. In fact, this information must be refreshed about 16 times per second. DRAM chip circuitry is made up of one transistor and one capacitor for each bit of memory. When a bit is assigned the value of one, the capacitor is charged. Capacitors don’t like being charged and immediately begin to discharge thus losing their value of one. For this reason, they must be constantly recharged or refreshed. Another down side to this recharging is that the CPU cannot access the memory while it is being refreshed, and must wait. This waiting can create an overhead or loss of processing time up to as much as 10%.

In summary, DRAM is the accepted standard for memory because it is fast and cheap, when compared to other methods of storage, but is still slower than the CPU.

DRAM – Chips

DRAM chips come in a variety of sizes and speeds. We will need to separate the concepts of chip size, chip package and memory modules. First lets look at an individual chip. The first DRAM chips were measured in terms of kilobytes. For example, a 256KB chip contained an array of memory that was one bit by 256K bits. Remember, memory is installed in byte wide increments, therefore if you needed to install 256KB of memory in an 8088 computer, you would need to install 8 chips each 256K x 1.

256K Memory – One Byte

As the chip manufacturing technology improved, memory chips began to combine several single array chips into multiple array chips. For example, you might find a 256K x 4 chip. This means that it has an array of four columns by 256K rows. This single chip is equivalent to four 256 x 1 chips.

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In early computers, installing memory was quite a job, as we had to install individual chips. In today’s age of memory, several chips are combined onto a small circuit board to make up a memory module. These modules come in a variety of sizes and will be discussed in detail later in this section. The important thing to remember is how to determine how much memory is on a module. This is actually very simple. The modules will be listed as 4X32 or 8X36 and so on. First, we think in terms of megabytes, so the first number defines the size of the array as the number of rows (megabytes) times the second defines the width of the array or number of columns. To determine the size of a module, divide the number of columns by 8 (convert bits to bytes) and multiply that number by the number of rows.

For example, what does 4X32 mean?

This means 4 megabytes by 32 bits

Or

4 x 32/8 = 16 megabytes of memory

The following table shows some common module sizes.

Common DRAM Modules

Chip Total Memory

2X16 4MB

2X32 8MB

4X32 16MB

8X32 32MB

2X64 16MB

8X64 64MB

16X64 128MB

Try calculating the total memory in the table above. Did you get them right? If not perhaps you forgot to divide the number of bits (columns) by 8 to convert them in to bytes.

Another important aspect of memory is speed. This is sometimes referred to as access speed, the average time it takes to complete a read or write to the memory. When thinking of speed in a computer, the first thing that comes to mind is megahertz. In our discussion of processors, we rated them by their speed in megahertz. We also mentioned that DRAM is fast and it is, but not as fast as a CPU. All memory chips come with a

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speed rating. It is normally marked on the chip label. Sometimes it is part of the manufacturer number and difficult to find. It is not important for you to be able to decode these numbers, but it is important to check the specifications before purchasing. All product literature will list the size and speed of their memory modules. Memory chips are speed rated in terms of nanoseconds or billionths of a second. Typical memory speeds have been between 60 and 80ns (ns = nanosecond). Keep in mind, the higher the number, the slower the memory.

When purchasing memory, always purchase the fastest possible, but remember that the actual speed will be limited to the slowest modules in the computer. Therefore, if you purchase 60ns memory and add it to a machine with 80ns memory, it will run at 80ns. The speed rating is the maximum speed of the chip.

The following table shows the relationship between processor clock speed and memory access time:

CPU vs. Memory Speed

Clock Speed (MHz) Memory Speed (ns)

10 100

20 50

50 20

100 10

200 5

300 3.3

500 2

In the graph, you see the clock speed (MHz) and RAM speed (ns). Notice that as nanoseconds get smaller, clock speeds (MHz) get larger.

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Matching Memory Modules to Data Bus

By convention, memory is always considered in terms of a byte. In addition, in the section on data buses, we saw that buses are always measured in terms of a byte. An 8088 computer used an 8-bit bus or one byte. An 80286 computer used a 16-bit bus or two bytes. An 80386 computer used a 32-bit bus or 4 bytes. The Pentium computer uses a 64-bit bus or 8 bytes. In order for memory to work, memory chips must cover the entire data bus. There are two approaches to resolving this problem. One is to add more memory modules, and the other is to make memory modules with more chips.

The first approach to resolving this problem was to add enough memory modules to fill the data bus. This technique is called banking. In the graphic below, you will see an 8-bit bus and two 16-bit buses. One 30-pin SIMM that is 8-bits wide is required for an 8-bit buss and two 30-pin SIMMs are required for a 16-bit bus. On the other hand, you can use one 72-pin SIMM (16-bits wide) on a 16-bit bus.

Memory – One Bank

By adding additional banks, memory can be expanded further. These are designated as bank 0 and bank 1.

Memory – Two Banks

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To further show you how this works, look at the following graphic. It shows 1 megabyte of memory in four rows of 256 chips. What is important is how the rows are divided into banks for each bus architecture. You can see that an 8088 will need four banks of one row each and 80386 will need one bank of four rows.

Banking

To summarize banking there are a few guidelines you must follow:

• A row of memory is considered one group or module of memory.

• All rows in a bank must be either completely filled or completely empty and must contain identical chips.

• A bank is one or more rows of memory that collectively covers the entire data bus.

• Each bank is numbered, starting with bank 0.

• Memory must be added to each bank starting with 0 and all rows must be full.

• Always refer to the motherboard book for bank numbering and installation.

Reliability of Memory

While today’s memory chips are deemed very reliable, it was not always so. Earlier chip designs were prone to failure. To deal with the issues of chip reliability manufactures implemented a couple of approaches. The first was to ignore the problem, and just hope that the chips would be reliable enough to do the job. Second, they hoped that not too many would come back. This was no problem on the low-end of the computer market, but with high-end computers, this could present a problem. Imagine if your bank’s computer occasionally failed to calculate your bank balance properly. In low risk situations, no protection was cost effective.

The second method was to add an additional chip called a parity chip. This extra chip is called the parity bit. Parity works via additional programming that will examine each

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byte of memory and add up the number of 1s in the byte. Then by adding an additional bit (chip) they could change the value of the ninth bit such that the total number of 1’s for all nine bits is either odd or even. If parity is odd, the ninth bit will be one if the total of 1s in the other eight bits is even. If parity is even, the ninth bit will be one if the total of 1’s in the other eight bits is odd. If any of the bits are corrupted, the count will not be correct and an error will be detected. The down side of parity is that the additional chip will increase the cost of memory by about 12.5 percent.

Note: When purchasing memory modules, you will notice some with numbers like 4X9 or 4X36 instead of 4X8 and 4X32. These additional numbers are the parity chips and you will have to account for them when calculating total memory of the module. Note that the 4X32 chip went to 4X36, not 4X33. This is because there are 4 bytes across the chip and each one will require its own parity chip.

The third method of provided memory reliability is ECC or Error Correction Code. This is the successor of parity. ECC goes one step beyond parity and will actually correct a single bit error. Since about ninety eight percent of all errors are single bit, this method provides for reliable memory. This is a very complex process and well beyond the scope of A+. However, you should be aware of what it is and how it relates to parity.

Note: if your RAM is faulty, it can cause NMI (Non Maskable Interrupt) errors. AN NMI error is an error that demands the CPU’s attention right away. Specifically speaking, the most common cause is a parity error.

Beyond DRAM

DRAM has been a stable part of computer systems for a long time, but as with all things in a computer, there have been some improvements. Lets look at some other forms of DRAM and how they have improved memory.

FPM

Fast Page Mode DRAM is a variation of standard DRAM. Actually, the memory is the same, it is the way that memory is addressed that changes. Standard memory is addressed one row and one column at a time. With the original byte wide memory modules, this was the only way. With the new larger arrays, memory can be addressed one row at a time. Paging is the process of accessing memory in larger chunks. The memory is divided into groups from 512 bytes to a few kilobytes in size. The paging process enables access to data in these groups with fewer wait states for the processor.

EDO RAM

EDO or Extended Data Out RAM is an improved and faster version of FPM. It was designed specifically for Pentium systems. This chip provides improved performance by allowing the memory controller to begin a new address instruction while it is reading data at another address. This technique provides a published increased performance of twenty-two percent over standard RAM. Actual testing of the performance shows a real time increase of less than ten percent. As a computer technician, you must know that

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there are two conditions for using EDO RAM. First, the motherboard chip set must support EDO and you cannot mix EDO and standard memory. EDO memory works best on bus speeds up to 66MHz.

SDRAM

EDO RAM, while an improvement, was short lived and was replaced with SDRAM (Synchronous DRAM). With SDRAM, the speed of the memory is synchronized with the speed of the bus, thus significantly improving its speed. SDRAM will operate in the 8ns to 10ns range. Like EDO, the motherboard chip set must support SDRAM and you cannot mix it with other types of RAM. SDRAM is designed for the new 100MHz system buses. The good news is that SDRAM is still DRAM and is not significantly more expensive. Data is delivered in high-speed bursts.

DDR SDRAM

Double Data Rate SDRAM or DDR for short was designed as a replacement for SDRAM. It is very similar in function, but it doubles the speed of SDRAM by transferring data twice per clock cycle. Normally, data is only transferred on either the rising or the falling edge of a clock cycle, but DDR causes data to transfer on both edges. This allows speeds of up to 200 MHz. This same technology allows the new AGP technology to double performance over the older PCI bus technology.

DRDRAM

Direct Rambus Dynamic Random Access Memory or DRDRAM is a memory subsystem that consists of the RAM, RAM controller and the bus that connects the RAM to the CPU and other devices that use RAM. This technology delivers transfer rates up to 1.6 GB per second.

DRDRAM was formerly known as Rambus DRAM or RDRAM and is actually a revolutionary new design. Instead of working like conventional RAM, its technology performs more like a bus. It also uses both the rising and falling edges of the clock cycle to transfer data.

DRDRAM uses a 16- or 18-bit bus rather than 8-bit like DRAM. This increased speed makes it ideally suited for today’s visually intensive applications such as 3-D graphics and streaming media. It was developed by Rambus, Inc. and more information on this exciting new technology is available at their Web site: www.rambus.com

The jury is still out on whether this technology will become the new standard, but Intel has announced that it is going to pursue this technology for use in all its future chipsets. Because of its proprietary design (it requires a special type of module call a RIMM or Rambus Inline Memory Module), other manufacturers would be required to pay licensing fees and this may end up to be a downfall for this technology (remember the MCA bus?).

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Synclink Dynamic RAM

Similar to DRDRAM, Synclink Dynamic RAM or SLDRAM also delivers high-speed memory, but without the proprietary design. It was developed by the SLDRAM Consortium, which consists of about 20 major computer industry manufacturers. It is an open standard and does not require the licensing fees that are required by the DRDRAM technology. This in itself may result in SLDRAM becoming the industry standard despite Intel’s support of DRDRAM.

This technology delivers greatly improved performance over the SDRAM technology without the use of a completely new architecture as does the DRDRAM. The specifications call for a 64-bit bus running at a 200 MHz clock speed. This is achieved by all signals being on the same line and thereby avoiding the synchronization time of multiple lines. Like DDR SDRAM, SLDRAM can operate as twice the system clock rate giving it an effective speed of 400 MHz.

Special RAM

One of the inherent problems with DRAM has always been the issue of refresh rates and its impact on speed. Another type of available RAM does not have this problem; it’s just costly. A SRAM chip will be up to 30 times larger (in size) and 30 times more expensive than DRAM. It is called SRAM or Static RAM. Remember that DRAM is dynamic and needs to be refreshed and SRAM is static and does not need to be refreshed. Electronically, SRAM does not use any capacitors to hold the 1s for a bit. Instead, it uses an arrangement of six transistors. The advantages of SRAM are that it causes no wait states for the processor and is therefore significantly faster. They can operate in the 2ns range and thus keep up with a 500 MHz processor.

Because of its cost, SRAM is used for special memory called cache. Cache is defined as a place to hide or store things. In a computer, cache memory is a place for the CPU to store important data that it needs to have quick access to. Since this memory is so much faster, the overall performance of a machine can be dramatically improved by using a small amount of cache memory.

Caching

Cache memory in a computer is found in three types, designated as L-1, L-2 and L-3. L-1 cache is called internal or integral cache. It gets its name from the fact that it is integrated into the processor chip. This is the fastest memory in the computer because it will run at the speed of the processor. L-2 cache is the second fastest memory in the computer. It is sometimes called external cache because it can be external to the processor and runs at the speed of the bus. L-2 is also expandable. Many motherboards provide the option of adding additional cache thus keeping the initial cost lower. L-3 cache is additional cache on the motherboard located between the CPU and the main memory. If the CPU includes L-2 cache (newer models are starting to do this), what was designated as L-2 cache on the motherboard becomes L-3 cache.

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Write-Back Cache (Copy-back cache)

Changes to data stored in the L1 cache aren’t copied to main memory until it is unavoidable.

Write-Through Cache

Data is written to the L1 cache and main memory simultaneously. This allows for better performance but can be risky if there is loss of power or a system crash.

The following table shows the relationship between L-1 and L-2 cache speeds.

Cache Speeds

Processor Speed (MHz) L-1 Speed (ns) L-2 Speed (ns)

100 10 30

200 5 25

233 4 15

300 3 6

400 2 5

Working with Memory

The third element in working with memory is memory modules. We have discussed the concepts with various memory chips, but now we need to look at the more practical side of memory. That is, how do you determine what memory to install in a particular computer? The answer to that question is dictated by the architecture of the computer in question. The three elements that establish the type of memory modules are the size of the address bus (maximum amount of memory that can be installed); the size of the data bus (number of rows and banks); and the motherboard chip set (type of RAM that can be used). As we mentioned in our previous examples, in the early 8088 computers we actually installed individual chips. These chips are called DIPPs (Dual In-line Pin Packages). This is a standard format of integrated circuits, which is a small rectangular plastic case with two rows of 8-pins each. Installing these chips was challenging as you must align all the pins and carefully push them into place. Installing 1 megabyte of RAM with 256K chips requires 32 chips. This means 512 pins needed to be aligned with out bending or breaking. Just imagine installing 32 megabytes with 256K chips (125 chips – 2,000 pins)!

As memory technology responded to the needs of computers, memory chips were bundled into modules. A module is defined as a small circuit board with memory chips. The number of actual chips is unimportant, but you must know the width of the module

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so you can determine how many rows (modules) you will need to fill a bank. Lets now look at the various memory modules, as they developed to respond to address buses and data buses.

DIPP Chip

SIPPs

A SIPP (Single In-line Pin Package) was the first attempt at making the installation of memory simple. Designers simply took the row of 8 memory chips (9 with parity) and soldered them on to a circuit board. On one edge was a row of pins that could be inserted into a connector. Now instead of installing 8 chips, you needed to install only one module with 30 pins.

SIPP

CAUTION: SIPPs have a row of pins along one side. These pins are easily broken and care should be taken when installing them.

SIMMs

SIMMs (Single In-Line Memory Modules) – are an improved version of the SIPP. These modules were much more popular than their predecessor was, since they did not have any pins. Instead, the edge of the module had fingers or contacts making installation a snap. They literally fit into a slot at an angle and then snap into position. Another improvement was a reduction in the number of chips required. Remember, original memory chips were only one bit wide, but improvements in manufacturing technology allow for integration of several into one package. SIMMs come in two varieties, 30-pin and 72-pin.

The original SIMM was designed for use on an 8-bit data bus. These are obsolete today. In order to use them on a 64-bit Pentium system, you would need eight SIMMs per bank.

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30-Pin SIMM

72-pin SIMM

The 72-pin SIMM rapidly replaced its predecessor. The main difference is that the 72-pin SIMM is designed for a 32-bit data bus. A 64-bit Pentium bus will need only two of these for one bank.

72-Pin SIMM (Two 1MegX4 chips and one 1MegX1 chip)

DIMMs

The next packaging introduced to the market was the DIMM or Dual In-line Memory Module. Just like its predecessor, the 72-pin SIMM reduced the number of slots you need to fill on a 32-bit data bus. The DIMM reduces the number of rows on a 64-bit data bus to one. These packages have 84 pins, but each side is a separate pin, giving a total of 168-pins. One of these chips can fill a memory bank.

DIMM Module

SoDIMM (Small Outline Dual In-line Memory Module)

SoDIMM is a DIMM module used in laptops. They have a more compact design.

MicroDIMM (Micro Dual In-line Memory Module)

MicroDIMM is a DIMM module introduced in 2000 that is used in notebook computers. They have 144 pins and have a 64-bit data path. MicroDIMMs are available in PC100 SDRAM. It functions at a speed of 7ns and a frequency of 100 MHz. It operates at 3.3v and a bandwidth of 2.1 Gbps.

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MicroDIMM Module

RIMMs

The Rambus Inline Memory Module is the latest in RAM technology. It conforms to the DIMM form factor, but it is not pin compliant. RIMMs utilize 184-pin edge connector pads and are suitable for use with 184 or 168 contact RIMM connectors. The important things to remember about RIMM modules are that they may only be used on motherboards that support them (have RIMM sockets) and are not backwards compatible.

RIMM modules are also different from DIMMs in that they are covered with a heat spreader. Since they are extremely fast, more heat is generated. Up to three RIMMs can be used on a PC desktop motherboard and RIMM continuity modules are inserted into unused sockets to maintain channel integrity.

The Rambus SO-RIMM Module is a general-purpose, high-performance memory module suitable for use as system memory in mobile systems and other small form factor systems.

RIMM Module

Note: Chip creep can occur from heat, which can cause RAM to become unseated.

Installing Memory

One of the most common jobs of a computer technician is to install RAM. It seems that computers never have enough RAM, and increasing RAM is often the best way to improve the performance of a slow computer. Doubling the amount of RAM can actually double the performance of a computer. A slow processor with lots of memory will outperform a fast processor with a minimum amount of memory.

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Before replacing or adding memory, you will need to prepare a strategy. You should never go out and purchase memory without first knowing exactly what you need. There are so many combinations for each computer that it would be almost impossible to predict the correct solution. The best strategy is to look first, then check the motherboard manual, and finally, purchase the required memory. Looking means to remove the cover from the case and look inside. There is no substitute for this.

The following are several things to consider before starting the upgrade.

• Are there any free slots on the motherboard?

• What types of slots are used? There may be more than one – for example SIMM and DIMM.

• Can you use EDO or SDRAM?

• How many modules will you need to fill a bank?

• Does the motherboard already have onboard memory (soldered to the motherboard)?

The best resource for confirming memory is the documentation that comes with the motherboard. Once you have determined the correct modules to install, the process of physically installing is simple.

When installing SIMMs or DIMMs remember:

• Unplug the computer from the wall socket.

• Always use the appropriate protection from ESD (see chapter on basic electricity).

• Always handle SIMMs carefully – you should never touch the chips or the circuitry. Always handle them by the edges.

• All SIMMs have a key on one side that prevents them from being installed improperly. This key will fit a post in the memory slot. Since it is off-center, you cannot install them backwards.

• You may have to remove or move some wires to gain access to the memory slots. Be sure to record the locations if you have to move them. You want to be sure to return them to the correct location.

To install a SIMM, hold it at a 45-degree angle and insert it into the slot being sure that the key is properly located.

When you are sure that the SIMM is correctly inserted into the slot, rotate it upright until it snaps into place.

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Installing SIMMs

After the memory modules are installed, replace any cables or other parts that you may have had to move.

Turn on the computer. Watch the RAM counter during the POST test. It should count up to the new value. If the RAM value did not change, check the following:

• Make sure all the modules are property seated in their slot.

• If you added memory to a free bank, make sure that the bank is not disabled. You will need to check for jumpers or perhaps the CMOS setup.

• Check to make sure that you purchased the correct memory modules. Perhaps they are EDO and your system will not support them.

Handling Memory Problems

Computers cannot operate without memory. Therefore, if the memory fails, the computer will fail. Fortunately, memory chips are reliable and once properly installed, rarely fail. Memory problems will manifest themselves in one of two ways. If they are produced by a hardware failure, they will be reproducible. That is to say, they will occur at the same place every time. Typically, these errors will show up during boot. Any error message that includes the word “parity” is most likely caused by bad memory. If the parity error happens at a different address each time, then suspect another problem like a bad power supply. In addition, hardware errors will show up as some form of a BIOS error such as memory mismatch or a series of beeps. Unless you have some sophisticated equipment that will test every bit on the memory module, the only way to resolve these problems is to replace each module one at a time with a known good one until the problem goes away. Of course, you could replace all the memory and be done with it.

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Intermittent memory problems are very difficult to resolve. Since you cannot reproduce the error, you will not be able to isolate it. You will also never be sure the memory is the problem or the symptom of a problem. In these cases, you have two choices. Replace all the memory and hope for the best or put up with the annoyance until it completely fails.

Logical Memory

Thus far in this chapter, we have been discussing physical memory. We have seen how memory works and how it is addressed. Now we need to look at how memory is used or allocated for use by the CPU and other components of the computer. Again, we must regress back to the early 8088 computers to gain a better understanding of how memory is allocated. The 8088 computer used a 20-wire address bus that limited the maximum amount of memory to 1 megabyte. This is often referred to as the DOS limit. Since memory was so limited at that time, it was very important to reserve portions for critical operations of the computer. To get a better understanding of how this works, a standard model called the “MS-DOS Memory Map” was created. This map as shown below divides this first megabyte into 16 blocks of 64 KB each. It further divides these blocks into two groups called conventional (640 KB) and reserved (384 KB) memory.

Memory Map

Its hexadecimal number or range defines memory, throughout the map. Notice that the memory starts from the bottom as 0MB or 00000h and continues up to 1MB or FFFFFh. The conventional memory area 0MB (00000h) to 640 K (9FFFFh) is the area dedicated for the user. It is within this portion that all applications and other program functions operate. The very first block at the bottom, 0 to 64K is used to load the DOS operating system.

The reserved memory area is just that, reserved for special purposes. To confuse matters, this area is also called the Upper Memory Area and Upper Memory Blocks. Don’t let these terms confuse you as they are often used interchangeably. This memory contains six of the memory blocks and has the address names of A0000h to FFFFFh. As shown in

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the graphic below, some of the blocks are used for designated purposes and the operator can designate a few as well.

Notice that video RAM is allocated to the bottom two blocks of the upper memory (A0000h to BFFFFh) and that the Motherboard BIOS is allocated the top position (F0000 to FFFFFh). The user can allocate the middle section.

EMS – Expanded Memory System

It did not take long before there just wasn’t enough memory. As more and more applications required more and more memory, 1 megabyte became a serious restriction. Three of the more prominent software manufactures (Lotus, Intel and Microsoft) got together and found a way to get 32 MB more memory. This technology has three names: LIM in honor of the creators, EMS or Expanded Memory System, and just plain old expanded memory. Just like the names for reserved memory, don’t let these names confuse you, they are all the same thing.

Expanded memory works by first installing an expansion card with additional memory chips. Then by loading the appropriate drives, a window (not a Microsoft Window) is created through one of the available upper memory blocks. Then by swapping 16 KB blocks or pages of memory between the Upper Memory Block and the memory card, additional memory can be accessed. Up to four 16 KB pages can be swapped at a time through this window.

EMS

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EMS did not live long, as computer technology increased the address bus size, thus allowing for access to additional memory. However, the need for EMS still existed to support some software applications. To get around this, you can run a DOS EMS emulator. This will allow for a portion of expanded memory (see next section) to look and feel like EMS so the software will run without the expansion card. In Volume II, we will discuss how to use DOS, but for purposes of reference, here are the commands to activate EMS. These commands are placed in the CONFIG.SYS file.

Device=c:/dos/emm386.exe

Dos=umb

By adding the last command, DOS drivers and any TSR (Terminate and Stay Resident) programs will also be loaded into upper memory. If you want to load just DOS drivers and TSRs, use this command:

Device=c:/dos/emm386.exe noems

Dos=umb

Extended Memory

With the release of the 80286 came a completely new way of using memory. First, this machine uses a 24-bit address bus. If you recall, this means that the CPU can now address up to 16 megabytes of memory. This is way above the DOS limit. Operating in memory above the 1-megabyte DOS limit is operating in extended memory. With this also came two modes of operation, real mode and protected mode.

In real mode, a 286 or better machine will operate just like an 8086 machine. This means that it would be limited to 1 megabyte of memory or less and would have to comply with all the limits thereof. When running in real mode, an application has full control of the computer and all the attached devices.

When running in protected mode, several applications can run at the same time and each is protected from the other’s memory. Also, with this mode came the once dreaded GPF or General Protection Fault. When this happened, one of the applications violated another’s memory and the system stopped.

In order for DOS to use this newfound wealth of memory, the appropriate driver still has to be loaded. Once again, by adding the appropriate command to the CONFIG.SYS file, DOS will have access to extended memory. That command is:

Device=himem.sys

As a bonus, we can also move most of DOS out of conventional memory and into the first 64KB of extended memory. To make this happen, use this command:

Device=himem.sys

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dos=high

If you want to use EMS, extended memory, and move as much of DOS out of the conventional memory as possible use these commands:

Device=himem.sys

device=emm386.exe

dos=high, umb

High Memory Area - HMA

Optimizing Memory

The first step in optimizing memory on a system is to determine what is already in use, and what is available. DOS provides a very useful tool for looking at the memory allocation within a computer. Even if you are running a Windows 9x machine, you can go to a DOS prompt and use this tool. The command to access this tool is MEM. Several options or switches can be used with this command. To access a list of these switches, type the command MEM /?.

MEM.COM

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Note: If you are using IBM’s PC-DOS, use the QCONFIG.EXE program in place of MEM.

Most systems have numerous device drivers and TSRs (Terminate and Stay Resident) programs loaded from CONFIG.SYS and AUTOEXEC.BAT. These programs are by default loaded into conventional memory taking up valuable space. Memory management techniques are used to load these device drivers and TSRs, from the conventional memory into the Upper Memory.

To find which device drivers and TSRs are loaded, use the MEM command with the /c (classify) switch. This will determine how much conventional memory a certain real-mode program is using.

MEM /C

Another useful tool for determining the amount and allocation of memory is to use the “Memory” button provided with the MSD program (Microsoft Diagnostics). MSD is a DOS program and is not available with Windows 9x. You can however, copy this program to a bootable DOS diskette. Then boot the computer from the diskette and run MSD.

MSD

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Note: Hexadecimal notation is used; “U” represents areas of the UMA, which are used by TSRs and device drivers.

Once you have determined how much memory is available, you will need to move a few things around to free up additional conventional memory. Modifying the CONFIG.SYS file does all this.

Note: The CONFIG.SYS file is a text file and can be edited with any text editor program.

This first thing to do is make sure that extended memory is activated and to load DOS into HMA as previously described. Next, you can move some TSRs and other drivers into upper memory. This is called loading them high. The command for this is DEVICEHIGH+<drivername>. One rule when editing the CONFIG.SYS file is that the DEVICE=C:\DOS\HIMEM.SYS must be the first statement in the file.

Note: Any drivers that are loaded from the AUTOEXEC.BAT file can be loaded high by using the LOADHIGH or LH command.

If you are using version 6 of either Microsoft DOS or IBM DOS you can automatically configure memory. The programs to accomplish this are MEMMAKER and RAMBOOST respectively. These are not perfect so be careful when using them. You might want to backup your existing CONFIG.SYS and AUTOEXEC.BAT files first. The only difference between the two is that RAMBOOST is a TSR and will automatically reboot and make changes if you alter the CONFIG.SYS or AUTOEXEC.BAT file.

Another form of optimizing memory is to shadow the BIOS. BIOS routines are stored on ROM chips, but also have allocated space in the RAM reserved memory area. Actually copying the data out of the BIOS ROM and into RAM speeds up processing. Since RAM is faster than ROM, anytime an application needs to access the BIOS, it can get it faster from RAM. Shadowing is enabled via the CMOS setup utility.

Shadow RAM

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Summary

This chapter focuses on the memory. When operating a computer we need to retain data in temporary storage in order for the processor to function. Today, there are many forms of memory, (RAM and ROM) with which a PC Technician needs to be knowledgeable about. Memory modules, such as SIMM, DIMM and RIMM are also important concepts that you will be dealing with both on the exam and in the real world. The following summarizes the information presented:

• Memory comes in many sizes and shapes.

• Installation of memory (RAM) is easy. However, you must be able to match the size and configuration of the memory chips to the motherboard.

• The width of one bank of RAM equals the width of the external data bus divided by the width of the SIMM chip.

• There are two types of cache memory (L-1 and L-2).

• Understanding memory allocation and the different memory locations is key to optimizing a computer’s memory.

• RAM chips come in many sizes and shapes. It is important for the computer technician to be able to identify the different types and calculate how many chips, banks or rows of memory modules are needed to upgrade a computer.

• RAM comes in many different types, be sure to understand all the RAM types, their uses and the form of module used.

• The number of SIMMs required is based on the width of the data bus.

• Memory (RAM) is allocated into different parts for the CPU to use. A computer technician uses a memory map to describe how memory is allocated. Hexadecimal numbers are used to identify the location of memory on a memory map.

• DOS can only access the first one Meg of memory.

• There are several tools like MEM.COM to identify memory allocation in a computer.

• A computer technician must know the difference between conventional and reserved memory.

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KEYWORDS Exercise

Define each of the following keywords. Hint: There’s a glossary in the back of this book.

Keyword Definition

DDR SDRAM

DIMM

DRAM

DRDRAM

EDO RAM

Fast Page Mode DRAM

RAM

Rambus SO-RIMM

RIMM

ROM

SDRAM

SIMM

SIPP

SLDRAM

SRAM

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Review Questions Chapter 5

1. What is Conventional Memory? Expanded Memory? Extended Memory?

2. What is the difference between ROM and RAM?

3. One Kilobyte equals how many bytes?

4. How many 30-pin SIMM boards are required to make one bank of memory on a 486 computer?

5. What is the difference between “write through” and “write back” cache?

6. What is access speed?

7. What is the major difference between SIPPs and SIMMs?

8. What is cache memory?

9. One of the differences between DRAM and SRAM is that SRAM does not have to be refreshed. What does this mean and how does it affect the cost of each?

10. DRDRAM has an access speed of up to ___________.

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Chapter 6 – Power Supplies

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Chapter 6 – Power Supplies

The power supply is the least problematic part of a computer. For all practical purposes, one size fits all. Laptop power supplies and those designed for unique computer cases are the exception. A power supply takes power from a local source (wall outlet) and converts it to +/- 3.3 to 5 volts DC for on-board electronics and +/- 12 volts DC for motors and hard drives. Many newer power supplies have a universal input and will work with either 120 VAC 60 Hz (US standard power) or 220 VAC 50 Hz (European/Asian standard). When replacing a power supply, there are three things to consider: size, wattage and connections. This chapter covers the basics of power supplies including troubleshooting.

Matching Size to Case

Power supplies are available in “standard” sizes and shapes. The following are eight common power supply names:

PC/XT – Basic power supply

LPX - slimline

AT/Desk – AT Desktop ATX (mini)

AT/Tower – Full Size NLX – low profile

Baby AT – Shortened version of AT

SFX – for small systems

The most common is the “ATX Mini”, which will fit most desktop or mini-tower computers. The ATX mini comes with power ratings of 200 to 400 watts. When you purchase a new case for a computer, it will include the power supply. The name is not nearly as important as the power it produces and the physical size of the box. The size of the unit will be based on the number of hard drives and other peripherals that can be installed. While a “standard” mini-tower may have a 200 to 300 watt power supply, a larger full size tower may have a 500-watt power supply.

The best thing to do when replacing a power supply is to take the old one and compare it to the new one. As long as it is physically the same and will produce at least as much power, it will work.

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How much power is enough?

Power supplies are rated by the maximum power (Watts) that they can produce. A watt is a unit of electrical power equivalent to one volt-ampere (Volts X Amps). If you take the input voltage and multiply it by the current used, you will have an estimate of the power in watts. It is important to keep in mind that the power supply must produce at least enough energy to operate all the components of the system at one time. During boot or computer system startup, many components will require additional power to get going. On average, a computer will use 115 to 130 watts while running and up to 200 watts when booting. If a computer does not have enough power, it could reboot unexpectedly. The following table can be used as a guide for calculating the power requirements of a computer:

Estimated Power Requirements

Computer Configuration Estimated Wattage

1 floppy disk drive

1 hard disk drive

200

2 floppy disk drives

1 or 2 hard disk drives

1 CD-ROM or tape drive

1 Sound Card

250

More than 2 floppy disk drives

More than 2 hard disk drives

More than 1 CD-ROM drive

300

Getting Connected

A power supply, as far as a Computer Technician is concerned, is a small box with wires on both ends. One end is the input side and a standard 120 VAC power cord. Sometimes you may find a switch so that you can change the input between 120 and 240 VAC (US standard and European Standard). This power cord can be either hard wired or a standard power cord.

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Power Supply Connectors

On the other end are the output connectors. This will be a bundle of wires (20 to 30) terminated with several connectors. Two connectors called the P8 and P9 connectors will each have six wires per connector. These are used to provide power to the motherboard. The other connectors, (P10 thru P13) will have four wires per connector, and are used to provide power to the floppy drives, hard drives and other drives (CD-ROM) as necessary.

P8 & P9

These are perhaps the most important connectors on the power supply. If installed improperly onto the motherboard, the motherboard will be damaged. Fortunately, with a little care, they can be properly installed every time. Since the two connectors are identical, there are two problems to consider when installing them. First, they could be installed backwards. While this is possible, it is not likely. The P8 and P9 connectors are numbered and keyed. These keys or notches will prevent all but the most insistent from installing them backwards. You would have to force them on the connector, so if it seems difficult to make the connection, it is most likely wrong. The second problem is installing them into the wrong connector. This is more likely to happen than installing them backwards. If they are installed in the wrong connector, they will damage the motherboard and other components. The P8 connector provides the 12-volt power and the P9 provides the 5-volt power. If the 12-volt power is connected to devices that only use 5 volts, there will be smoke. To prevent this, all you have to do is pay attention to what you are doing and follow these two simple rules.

The P8 and P9 connectors are numbered and are installed into the P1 and P2 power connectors respectively. Look for the numbers on the connectors and on the motherboard for guidance.

Always install P8 and P9 with the black wires together. This is known as the “black on black” rule. Both connectors have a pair of back wires. If you hold them so that the four black wires are side by side and the keys on the connectors are on the same side, you cannot go wrong.

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P8 & P9 Connectors

Note: Pentium II and later motherboards have incorporated the P8 and P9 connectors into one large connector that will eliminate installing them incorrectly. However, P8 and P9 installation is an important concept when dealing with older technology.

In addition to the black ground wires, you will find yellow, blue, red and white wires. The following table shows the expected values for the voltages on each of the other wires. The ground wires are considered 0 volts and all measurements are based on measuring the voltage between the black wires and one of the colors.

Color Coded Power Cables

Cable Color Supply In Tolerance

Yellow +12 ± 10%

Blue -12 ± 10%

Red +5 ± 5%

White -5 ± 5%

Black Ground N/A

NOTE: If you have occasion to service a computer that uses a proprietary design, you will no doubt notice that the power supply and connectors are not standard. Your only recourse is to purchase replacement parts from the manufacturer and follow their instructions for installation.

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You must install P8 and P9 so that the two black grounds on each connector are together! Installing them backwards can damage your motherboard and/or the power supply. The following picture shows the connection of the P8 and P9 wires to a motherboard.

Connecting P8 & P9

Molex or mini

In addition to the motherboard connector, a power supply output will have at lease four other connectors. These are used to power the floppy drives, hard drives, or any other internally installed drives. Peripheral hardware can connect to two standard types of connectors. They are called the Molex and the mini.

The early power supplies used only the Molex connector. They were used to power up to two 5-¼ inch floppy drives and up to two hard drives. These connectors provide both 12v and 5v power to the drives. The red wire is used for 5 VDC and the yellow wire for 12 VDC. The two black wires are ground. Like the P8 and P9 connectors, Molex connectors are keyed to prevent misalignment when connecting them.

Molex Connector

With the introduction of the 3-½ inch floppy came a smaller connector called the "mini.” The mini connectors work just like their predecessor but are smaller. They too are keyed to prevent improper insertion, but BE CAREFUL with a minimal amount of force you can insert them upside-down. Installing a mini incorrectly will destroy the device!

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Mini Connector (not to scale)

Device Connectors

Power Switch Connectors

Power switch connectors are highly variable and dependent on the case manufacturer. In general, they will come in two types. Either as part of the power supply, or remote to the power supply. If they are part of the power supply, they will be located on the back of the computer and you will not have to worry about them. Those that are mounted remotely could be of any size and shape. The only thing in common will be the colors of the wires. The blue and brown wires are the power directly from the wall outlet and are hot any time the power supply is plugged in. The white and black are the switched side and will be hot only when the switch is engaged. Warning, NEVER assume that a wire is not hot – TEST IT!

When things go wrong!

Power problems can come from one of two places. The first is the power company, and the second is the power supply itself. Let’s look at ways to deal with these problems.

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The Power Company

Power supply problems can originate from both internal and external sources. In addition to problems stemming from defective power supplies, many problems are related to the quality of the local power source. These problems can be spikes, surges, sags, brownouts and/or blackouts. None of these events can be controlled, but we can do a few things to protect our equipment and data:

Spikes and Surges A brief, but often catastrophic, increase in the voltage source (very high voltage for a very short duration). These can be caused by the power supply, but most often are caused by lightning strikes. A spike or transient is a very short over-voltage condition measured in nanoseconds, while a surge is measured in milliseconds.

Sags A brief decrease of voltage at the source that can cause computers to restart.

Brownouts If a sag lasts more than a second, it is called a brownout. The overloading of the main power source can cause brownouts. Some brownouts are “scheduled” by the Power Companies to prevent overloading of circuits and potential catastrophic failure of the system.

Blackout A complete power failure. May be caused by equipment failure (local or regional) or accidental cutting of power cables. When the power comes back on after a blackout, there is danger of a power surge.

Surge Suppressors are used to filter the effects of voltage spikes and surges. They are good for cleaning fluctuating commercial power sources. Surge suppressors filter incoming power signals to smooth out variations. They are available from local computer dealers and super-stores. A good surge suppressor will protect your system from most problems, but remember you get what you pay for. If you purchase the “econo-brand,” it may not work when you need it the most. Look for performance certification and power ratings when evaluating surge suppressor quality. These units protect up to a point; however, for complete protection of fluctuations, plus complete power outage protection, the Uninterruptible Power Supply (UPS) provides the most complete coverage.

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THE BEST DEFENSE AGAINST VOLTAGE SPIKES CAUSED BY LIGHTNING IS TO UNPLUG YOUR EQUIPMENT DURING STORMS OR LONG PERIODS AWAY FROM YOUR OFFICE OR HOME.

Uninterruptible Power Supplies (UPS) (sometimes referred to as a battery backup) will provide protection from all forms of power fluctuation and failure. When properly installed between your computer and the wall outlet, these devices will protect from surges and act as a battery when the power dips or fails. They will also provide a warning that the power is out of specification. Many of the more expensive models can also interact with the computer and initiate a safe shutdown in the event of a complete power failure.

If you want to make sure that your power is “pure”, use a line conditioner. Surge suppressors are considered a low-end version of this type of device. Line conditioners cannot help you in a blackout, but they are very good against other power fluctuations.

Note: When considering what devices to connect to a UPS, never choose a laser printer. They are power hogs and are not frequently damaged by power outages.

When purchasing a UPS, consider:

• How much peace of mind do you require?

• How much protection does your equipment need?

The VA rating (Voltage x Amps = Watts) - must be enough to supply all the equipment with power long enough to safely shut down the system. The easiest way to calculate this number is to add up the power rating (Watts) for all pieces of equipment that are to be connected to the UPS, as shown in the following table.

UPS Power Calculation

Device Power Rating

(Watts)

Connected to UPS

Power Required

Computer 250 Yes 250

Monitor 80 Yes 80

Printer 200 No 0

External Modem 5.5 No 0

External Back-up Drive

50 Yes 50

Total 585.5 - 380

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In this case, a minimum 600 VA UPS would be required if all equipment is connected, or a minimum 400 VA UPS if only the computer, monitor and back-up drive are connected.

The Power Supply

The most recognizable power supply problem is a complete failure of the power supply. This is easily detected – nothing will happen. When there is apparently NO power, be sure to check the power source and the plug (at the outlet and the computer). The symptoms of this type of failure are:

• No noise, lights, and no fan running

• Blown fuse or circuit breaker

• Smoke

Power supplies can be the source of intermittent failures such as memory loss. These will show up as a parity error. If you start to get parity errors, there is one way to isolate the memory from the power supply. Memory parity errors will always be in the same place; power supply parity errors will be random. Always write the error code and keep a running list. Intermittent errors occur when a power supply begins to fail. The output voltages will drop. When it approaches the point of complete failure, any sudden increase in load (hard drive start ups, etc.) will cause the power to drop below the minimum requirements. This may be of a short duration, but during that time, an error could occur. Therefore, if you are experiencing intermittent failures, and you cannot relate them to any particular event, check the power supply.

Here are some tips concerning when to suspect power supply problems:

• Power-on failures or lock-ups

• Spontaneous rebooting

• Hard disk and fan stops spinning

• Overheating caused by no cooling fan

• Electrical shocks on the system case

When a power supply fails, replace it!

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Summary

Even though a power supply is reliable and has no user serviceable parts, a Computer Technician must understand them. The following summarizes the key points of this chapter:

• Either internal or external forces can cause power supply problems.

• There are several devices available for protecting against external power problems.

• Power supplies come in several sizes and shapes.

• A power supply must be capable of handling the requirements of the computer and all internally attached devices.

• The key to specifying the proper size power supply for a computer is to sum up the power of all the components. Be sure to add extra power for boot-up.

• Electrical power is measured in Watts.

• Proper installation of the P8 and P9 connectors is important to prevent damage to the motherboard. The black (ground) wires must be installed together.

• Molex and mini connectors are used to connect power to devices such as floppy and disk drives.

• The incoming power to a computer must be managed in order to prevent damage and or loss of data. Surge suppressors will eliminate over voltages while a UPS will eliminate both over voltage and under voltage situations.

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KEYWORDS Exercise

Define each of the following keywords. Hint: There’s a glossary in the back of this book.

Keyword Definition

ATX Mini case

Blackout

Brownouts

Mini connector

Molex connector

Sags

Spike

Surge

Surge Suppressors

UPS

Watt

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Review Questions Chapter 6

1. Explain the difference between spikes, surges, and sags.

2. What is the difference between a brownout and a blackout?

3. When you purchase a UPS, what is the most important thing to consider?

4. Will all surge suppressors protect from lightning?

5. What is the best defense against spikes caused by lightning?

6. What is the most important thing to remember when connecting a P8 and P9 connector to a motherboard?

7. What is the difference between the mini connector and the Molex connector?

8. What is the best way to make sure the power supply you’re going to purchase will match the one you are replacing?

9. What are mini connectors primarily used for?

10. A Computer power supply has both 5V and 12V outputs. The 5V is used to power _____________ and the 12V is used to power ___________.

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Chapter 7 – Storage Devices

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Chapter 7 – Storage Devices

The operation of a computer is based on its ability to manipulate and manage data. As time has progressed, both with the development of computers and evolution of information technology (IT), the need to store vast amounts of data has increased dramatically. The computer’s ability to store and retrieve data is second only to the motherboard and CPU in importance to the user. This chapter is going to explore the many ways that computers can store data. We will begin with the storage devices of the distant past and continue through today’s optical storage devices.

Punch Cards and Tape Drives

The first forms of mass storage were by today’s standards very crude but actually follow the same principles that are still used today. If you will recall from the first section of this course, we mentioned the Hollerith card, also known less formally as the IBM punch card. Also, recall our discussion on binary and ASCII code. If you look closely at the card, (see graphic below) you will notice twelve rows and eighty columns of numbers.

IBM Punch Card

Eight of these rows represent the eight digits of an 8-bit binary number. Each card will hold 80 bytes of data plus a few more bytes (the other rows are for special commands). Data is stored by punching out one or more of the holes in each column. When light is passed through the holes, a “reader” will recognize the light as a one or ON. Programs or data for use by the computer were actually written by programmers on a separate machine. A program or data bank would consist of a stack of cards, which when fed sequentially into a reader that would load a program or data one byte at a time. This system worked just fine as long as no cards were damaged or lost.

The next level of data storage was the magnetic tape. Instead of having holes to pass light through, magnetic ones and zeros were recorded sequentially. Then, by running the tape, these ones and zeros could be loaded into the computer just like the data from the card reader. This technology was in fact no different from a standard tape recorder. Many of us may still remember the old Radio Shack TRS-80. The first models had no drives but came with a connection for a tape recorder.

Both of these technologies have two major drawbacks, speed and data access. The speed was limited by the mechanical action required to load a stack of cards and read them or to

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run a tape from one end to the other. The biggest problem was actually the fact that both of these technologies are linear. This means that you must start from one end and run through all the data until you find the data for which you were looking.

While the use of punch cards for storing data has virtually disappeared, the technology for storing data on tape has advanced. The only difference is that the focus of using tapes is on archival data rather than data that is accessed on a regular basis. They are also used frequently to backup entire hard drives. In both of these cases, tape is a good choice as the data is written and read in a stream of bits sequentially from beginning to end.

Microsoft provides, as a standard part of its operating system, drivers and software to backup data to a tape drive. To use this utility, you must first have a tape drive installed, then go to: Start>Programs>Accessories>System Tools>Backup.

Installation

Tape drives can be installed as an internal IDE device, an internal or external SCSI device or an external device connected to a parallel port. This installation process is the same as for any of the above-mentioned devices and will be covered in detail later in this chapter.

Floppy Drives

The floppy disk drive is perhaps the most stable and simplest computer component to install and maintain. What made the floppy drive so popular as a replacement for the tape drives were its speed and the ability to randomly access any files or data stored on them. The floppy disk drive is the most basic of the input/output devices and is perhaps the only component that has retained its original technology. Other than increased storage capacity, the floppy disk drive still works essentially the same (cabling and BIOS configuration) as it did when it was first developed.

IBM developed the first floppy disk drives. They were used on the IBM System 370 machines that came out around 1972. These drives used 8-inch floppy disks. The 5.25-inch floppies that were familiar on the early personal computers came later. Floppies were included in personal computers before hard drives mostly because they were relatively inexpensive.

Floppy Disk Drive Basics

Floppy disk drives come in a variety of sizes and capacities; however, the cabling and BIOS configuration has remained essentially the same from the beginning. A floppy disk is made of a flexible plastic disk, coated in a magnetic material. To protect them from dust and physical damage, they are packaged in a plastic or paper case. The main advantage of using a floppy disk drive and a floppy disk is that it is a removable media. The data stored on a floppy disk can be moved from one computer to another as long as both have the same type of drives. It is a good idea to always keep two copies of any data file that you create (original and a backup). The floppy disk is the perfect media for data backup as long as the file sizes remain small.

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5 ¼” Floppy & 3 ½” Floppy

Floppy Disk Capacities

Diskette Size Capacity

5 ¼” 160 KB Single Sided Single Density – The first model

5 ¼” 360 KB Double Sided Single Density

5 ¼” 720 KB Double Sided Double Density

5 ¼” 1.2 MB Double Sided High Density

3½” 720 KB Double Sided Double Density

3½” 1.44 MB Double Sided Double Density –Today’s Standard

3½” 2.88 MB Dual-Sided Quad – This technology was never fully developed due to the CD-RW technology that was released at about the same time.

Floppy disks come in three physical sizes. The full-height, which are the older large 5-¼ inch drives, the half-height, which are typically the 3-½ inch drives, and the combo, which contains a 1.2 MB, 5-¼ inch and a 1.44 MB, 3-½ inch drive. Today, the 5-¼ inch floppy drive is considered obsolete, but many uses are still found for the 3-½ inch drives.

All floppy disk drives are connected to the motherboard (external data bus) using a standard cable. A standard floppy drive cable consists of a 34-wire flat ribbon cable with five connectors. Two of the connectors are 34-pin connectors used to connect to the 3-½ inch drives. Two are edge connectors (these connect to the edge of a circuit board) and are used to connect to 5-¼ inch drives. The fifth connector is used to connect to the motherboard. The cable has a seven-wire twist in lines 10 through 16. These twists

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separate the connectors for the “A” drive from the “B” drive. The “A” drive connectors are on the end of the cable. Even though there are four connectors, you can only use two, one for the “A” drive and one for “B” drive. It does not matter whether or not the drive is 3-½ or 5-¼ inch. The other wires carry data and ground signals.

Floppy Disk Drive Cable with a “twist”

Installation

Installing a floppy drive is a three-step process:

1. Physically install the drive.

2. Connect the cables.

3. Configure the drive.

Physically installing the drive is relatively easy. It will have side mount screws that match holes or slots in the mounting bay, which is part of the case. The biggest problem that you may encounter is installing any special brackets to accommodate physical differences in size, between the 3-½ inch drive if it is installed into a universal bay that will also hold a 5-¼ inch drive. A little patience and practice, and this will be no problem. You may also have problems with access to the mounting screws on some case designs. You may have to remove other components (like the motherboard) to get access to them.

Connecting cables is as simple as making sure that you use the right connector for the drive. In addition, you must be sure to connect the number one pin on the cable to the number one pin on the drive. The cable has a red wire on one edge, which designates the number one pin. The 5-¼ inch drives with the edge connectors are keyed so they will plug in only one way. You will need to be very careful with the pin connectors. They too are keyed, but you can easily overcome them and install the connector backward. The good news is that if a connector is backwards, it will not damage anything. If you install a new drive, and you notice that the indicator light comes ON and stays ON, the cable is most likely backward.

Configuration of floppy drives is easy. You need to know only two things. First, if you have only one drive, it must be connected as the “A.” Second, floppy drives must be enabled in the BIOS or CMOS setup. In the CMOS setup, you will see a listing for each

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floppy (or diskette). Just change it to the appropriate setting. Make sure that you choose both the drive and diskette size that match the drive you installed.

Floppy Set-up

The power connectors for the 5-¼-inch and the 3-½-inch drives are different. Typically, the larger 5-¼-inch drives use the larger Molex connector and the smaller 3-½-inch drives use the smaller Molex connector. The best method for determining what you need is to look. Both of these connectors are keyed to prevent improper installation, but the smaller one can be forced in backwards so you will have to be careful. By the way, on most drives the data cable pin number one is located towards the power connector.

Floppy Drive Cable Connections

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Maintaining a Floppy Drive

Floppy disk drives are highly susceptible to abuse-caused failure. With a little maintenance, they will provide years of service with no problems. Failures will come from two sources. First is just plain mechanical abuse. For example, when an operator forces a disk in backwards or inserts one with a damaged dust cover (the little metal sliding door on the disk). Exposure to foreign debris through the disk slot can cause excessive deterioration of the read/write heads. Computers installed in an industrial environment will require more maintenance and replacement.

The second cause of failure is cable connections. Many times after servicing other components (such as installing an expansion card), floppy drives suddenly stop running. Either the cable has been pulled loose or installed backwards. This can also occur just after relocating computers.

There is actually a third failure that looks like a bad floppy drive but is not. If you receive the standard error indicating that the computer cannot read the drive, the problem could in fact be a corrupt BIOS. BIOS makers often default the CMOS settings for the A: drive to 3-½ inch high density. With this BIOS, failure of the CMOS battery, or even accidental erasure of the CMOS, will still allow most floppies to work. Always double-check the CMOS. It is quick, easy and may save you time. It is possible for the CMOS to be corrupted by software, or a hardware conflict and yet appear to be OK. If all else fails, reset the CMOS and reinstall the set-up (check motherboard manual for jumper settings or disconnect the battery).

Note: Checking the status of the drive in the Windows 9x device manager can often identify a floppy problem, but not always. It is possible for Windows 9x to think that all is well while the BIOS is incorrect.

The bottom line with floppy drives is to keep them clean. There are many cleaning kits available in your local computer store. If a floppy fails, replace it – they’re cheap. It is a good idea to keep a spare one around just in case, and to use it for testing purposes. You can also use a lint-less swab with alcohol. To do this, you will have to remove the drive and take off its cover exposing the heads. This is better than using one of the kits, but may not be worth the time.

Note: The first thing to check when a floppy drive fails is the disk itself. Floppy disks are fragile and often fail.

Troubleshooting a Floppy

Problems with floppy drives can be divided into two categories. The first is when they don’t work at all, and the second is when you cannot read the drive.

When they don’t work at all, either you can’t hear it spinning and the light doesn’t come on, or the light is on and stays on. Floppy drive errors will show up during the POST portion of the boot cycle. Typically you will see “FDD Controller Failure” or “Drive A: Not Ready” errors.

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When you encounter these types of errors, consider these possible problems:

• The floppy disk

• The cables

• BIOS/CMOS

• The drive

• The controller

Always start with the simplest solution and then consider problems that require a more complex solution. The floppy disk itself may be corrupt in some way. If this is the case, use a known good floppy disk to test the drive configuration.

When the light is on and stays on, the most likely cause is a cable connection that is plugged in backwards. Check both ends of the cable and be sure that the pin number 1 is connected to the number 1 wire (the red one). If nothing happens, make sure that the cables are plugged in to the correct connector on the motherboard.

Next, check the CMOS setup. This procedure takes only a few minutes and is easy. It is possible for this to have changed back to the default setting or to simply be corrupted.

With the simple out of the way, the work begins. Next, check the drive itself. The best way to do this is to replace the drive with a known good one. Removal can be complicated on some machines so before you start, try connecting another drive to the power and data cables. If the new one works, you can remove the old one and replace it. Floppy disk drives are cheap and it always pays to have a good one around for just such occasions. Cleaning the drive could also resolve the problem.

The last component to check is the floppy disk controller. Generally, these controllers are very reliable and cause no trouble at all. The best method for troubleshooting a floppy drive controller is to replace it with a known good one. As simple as this sounds, it is not always that easy. Many motherboards integrate the floppy and hard disk controller as part of the board itself.

How do you tell if the controller is integrated into the motherboard? The answer is easy, take off the cover and look. If the controller is integrated, the data cables from the floppy disk will be connected directly to the motherboard. If the controller is not part of the motherboard, the cables will be connected to a circuit board installed in one of the expansion slots.

When replacing a floppy disk drive controller, keep in mind that most floppy disk drive controllers are bundled as part of an I/O card. These cards include some (usually all) of the following: communication ports (serial and parallel), game ports, and hard drive controllers.

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I/O Card with Floppy Controller

When adding a new controller card to a computer that has integrated controllers on the motherboard, you must disable any duplicate controllers. A computer cannot operate with two controllers for one device. Therefore, you must disable either the controller on the motherboard or the I/O card. This includes any duplicate communication and printer ports.

Note: If you are adding a new controller card and it happens to have additional communication or printer ports, you can take advantage of them as long as you configure them so they are different from the ones on the motherboard. We will learn more about configuration in the chapter on installing and configuring peripheral devices.

Frequently, floppy drives seem to fail right in the middle of a project. You will get an error that the software cannot access the drive. When these errors occur, they are symptomatic of either the floppy disk or an operating system problem. When you suspect a bad disk, you can take several approaches to resolve these problems.

• Always suspect a bad disk. Floppy disks are easy to corrupt. They are magnetic and if placed in a magnetic field, data can be altered. They are often left in hot vehicles that can cause physical damage to the disk.

• The easiest way to check a disk is to substitute it with a known good one (it must be a formatted disk). If you suspect a bad drive, never test with a disk that contains critical data. If the problem is the drive, it could damage the good disk.

• Another way to check a disk is to go to DOS and type the command DIR A:\. If a copy of the directory of files on the disk is displayed, the disk is OK. You may want to try this on a different computer to double check that the disk is good.

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• The problem may also be that the disk is good, but was formatted with a different file system. For example, if you try to read a disk that was formatted for Macintosh on a DOS based operating system, you will get a bad disk error.

Sometimes, an operating system can give an error indicating a bad disk or disk drive, but it is misleading. For example, you are working with your word processor and have been accessing a file on a floppy. All of the sudden, you need to get a file on another floppy and quickly make the change, but now can’t read the drive. This can happen because the operating system has created a virtual link to the file on the first disk and that link is blocking access to the drive from any other source.

Another very common floppy drive error is the “non-system disk.” This usually occurs when you try to boot a computer. The first place to look is in the floppy drive and remove any diskettes. Most disks that are used to hold data do not contain any of the files necessary to start a computer operating system. Later in this course, we will lean how to make a disk with the necessary files to boot. A bootable system disk is a very useful tool for any computer technician.

Hard Drives

Hard drives are mass storage devices. Virtually all computers today have at least one hard drive. Early hard drives were capable of storing only a small amount of data (10 MB), they were large, and expensive compared to today’s standards. At the time, the capacity was not a problem as the size of programs, and the work requirements put on them, were small by today’s standards. The first hard drive was about 4 inches tall, six inches wide; eight inches long and weighed almost ten pounds. A new hard drive can fit into your pocket and hold as much as 60 GB (with capacities of new drives increasing all the time). In this section, we will study hard drives from the early versions to today’s monsters.

Technology of Hard Drives

The first means of mass storage was the magnetic tape drive. Tapes are a good media for storing large amounts of data, however, as we said earlier, accessing data was slow and linear. Floppy drives resolved some of the problems with speed and data access, but had limited storage capacity. Hard drives were invented to provide a storage media that not only held large amounts of data, but were fast and allowed easy (random) access to that data. Using the floppy as a model, designers created a disk drive that could hold up to 10 Megabytes of data. At the time, this was a phenomenal amount of data. Since the diskette was not removable, or flexible, it became know as a “fixed disk” or hard disk drive (HDD).

The first IBM drives came out in the late 1970s and early 1980s and were code named “Winchester.” The original design concept included two 30 MB units in one enclosure: 30-30 (hence “Winchester”). The PC-XT was the first personal computer to include a hard disk. They were called “fixed disks” because they were not removable. The Winchester technology is the direct ancestor of all PC fixed disks.

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A hard disk operates on the same principal as a floppy disk. It has a spinning platter with a pair of read/write heads that traverse perpendicular to the rotation of the platter. What makes the hard drive different is that the platters are made of an aluminum alloy and have a thin magnetic media coating on both sides. These ridged disks are responsible for the higher storage capacities available on hard drives. First, designers can install more than one platter per drive, providing for more surface area and thus more storage. Second, they can spin the disk faster (3,600-10,000 rpm for hard disks as compared to only 300-600 rpm for floppy disks) and have better control over the read/write heads. This increased accuracy, higher speeds and more surface area allow for capacities in the gigabyte range instead of the 1.44 megabytes of a floppy. In addition, unlike the floppy drives, a hard drive assembly is housed in a sealed case, which prevents contamination from the surrounding environment. Keeping the inside air clean and all contaminates out is essential to long life of the drive. The tolerance or space between the surface of the platter and read/write heads is so small that the mere presence of a fingerprint can cause damage to the drive.

Read/Write Heads

The purpose of a hard drive is to achieve fast, random access to data stored on a flat surface. This is accomplished by using motion in two directions. The disk spins and the read/write heads are moved across the platter perpendicular to the motion of the disk. It should be obvious that the heads should not (and in fact do not) touch the surface of the platters while running. This would no doubt cause a catastrophic failure commonly known as a head crash. When this happens, the only solution is to throw the drive away and start over. Based on the Bernoulli principle (in any horizontally moving fluid the pressure increases as the velocity of flow decreases), the heads “ride” on a cushion of air. The interaction between the air in the chamber and the surface of the moving disk creates an interface of disturbed air that the heads ride on. Some designers in the hard drive business call this cushion of air an air bearing.

A critical element in hard drive design is the speed and accuracy of moving the heads across the platen. The read/write heads are mounted on an actuator arm that pivots so that the heads will traverse perpendicular to the rotation of the platen. Two designs have been employed that meet these requirements. They are stepper motor actuators and voice coil actuators.

Early hard drives used a stepper motor to move the actuator arms in fixed increments or steps. A stepper motor is a very precise motor that doesn’t spin continuously like we think motors should. It moves in discrete steps. They operate on pulsed electricity; each pulse will move the motor one step. For example, if you had a 360-stepper motor, it will rotate one degree per pulse or step. If you want to rotate the motor one half of a rotation, you would send it 180 pulses. If you were to grab the end of a stepper motor that was turning, you will be able to feel the pulsing of each step. Stepper motors are commonly used in modern robots and animatronics to create precise movements of mechanical arms.

While very accurate for these larger applications, stepper motors have some problems when used in hard drives. The biggest problem comes with heat. As the drive warms up, the physical expansion of the mechanical parts and the platter can change the positioning. Since the stepper can only move in predetermined steps, errors can occur. This is one

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reason why you should never try to run a hard drive (floppy either) that has been left out in the cold without giving it time to warm up to room temperature. The second cause of problems is time and physical deterioration of the components.

A third problem, read/write heads need to be “parked” when not in use with actuators. Remember, the heads do not touch the surface of the disk when it is rotating. However, when it stops rotating, they will contact the surface. This can cause damage to data. Therefore, when the drive is shut down, it must park or move the heads to an area of the disk that does not contain data.

NOTE: Older hard drives require that the heads be parked before moving the computer. It is recommended that you use the Park, Sit or Diskpark command.

The stepper motor drives of the past have pretty much been replaced with voice coil actuators. They are called a voice coil motor because they are designed using the same technology as the voice coil found in a stereo speaker. This principle uses a permanent magnet and a coil that is connected to the speaker’s paper cone, or in the case of a hard drive, the actuator arm. By passing electrical current through the coil, it generates a magnetic field that moves the actuator arm into the proper position. These motors have proven to provide a greater degree of accuracy, performance and reliability over their predecessor. The accuracy is achieved by providing a feedback signal from the drive to determine the actual position and make adjustments. Usually, one platen is used to provide this feedback data. This way, when heat causes expansion of the platen, the motor can compensate.

The biggest advantage of the voice coil motor is that you no longer need to park the heads. When the drive is shut down, (the power is removed from the coil) the actuator arm (which is spring loaded) moves back to its initial position thus eliminating the need to park the head. In a sense, they are self-parking.

Magnetically Storing Data

As we learned previously, computer data is stored in BINARY language. In the case of physical memory, it is the presence of voltage that represents the binary one in each cell of the memory array and the lack of voltage that presents binary zero. This works well, as long as there is electricity. For permanent storage, it will either have to stay connected to a battery or find some other way of recording ones and zeros. To the rescue is magnetic media. With magnetic media, the ones and zeros can be stored as either magnetic or non-magnetic areas on the drive surface. It is based on the principal of electromagnetism. This states that any time electric current flows through a conductor; a magnetic field is generated around the conductor. In addition, if a conductor is passed through a changing magnetic field, current is generated. The direction of the current is based on the polarity of the magnetism. Using these principles, magnetized and non-magnetized positions are created on the surface of the platter. The binary data is not stored as magnetic poles (plus or minus) but as flux reversals. The term flux defines a magnetic field that has a specific direction. A flux reversal is the change in polarity. Each bit written on the drive creates a pattern of positive-to-negative or negative-to-positive flux reversals on the medium.

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The read/write heads are used to read data from the magnetic surface or alter the surface for storage of data. They are made of U-shaped electrically conductive materials. By wrapping the conductive material with coils of wire, and passing current through the coils, a magnetic field can be produced that will write data to the disk. Alternatively, by passing the read head over the magnetic fields on the surface of the disk, a current is generated thus reading data from the disk. The process of reading and writing to a disk is called encoding.

The first method of encoding (back in the 70s) was called FM (Frequency Modulation). This method was commonly used on single density floppy disk (single density encoding). In order to achieve greater storage capability, an upgraded version called MFM or Modified Frequency Modulation was implemented. This technique allowed twice as much data to be stored on the same disk, thus the double density disks (double density encoding). MFM is the standard for floppy disk encoding today.

The next standard encoding method for hard drives was called RLL (Run Length Limited). Due to its increased performance and ability to store more data on a disk than either of its predecessors, this method soon became the standard for use on PC hard drive.

Two new technologies have been developed that have become today’s standard for data encoding on modern hard disks. These are PRML (Partial Response, Maximum Likelihood) and its successor EPRML (Extended Partial Response, Maximum Likelihood).

These methods are a complete departure from earlier technologies in the way that data is read and decoded on a disk. Instead of reading flux reversals, a controller employs sophisticated digital signal sampling, along with processing and detection algorithms to manipulate the analog data stream on the disk (the partial response). It will then determine the most likely sequence of bits this represents (maximum likelihood). EPRML is simply an improved way of doing this.

This sounds like a strange and unreliable way to read data on a hard disk, but is the standard used currently.

Hard Disk Architecture

In order for data to be stored and retrieved on the surface of a hard disk, the data must be organized. This organization will determine two things. First, is the maximum amount of data that can be stored, and second, how that data is retrieved. As we learned, hard drives are composed of one or more disks or platters on which data is stored. The physical organization of data on these platters if often referred to as the logical geometry of a hard drive. It is this logical arrangement of data that determines the maximum storage capacity of the drive.

The logical arrangement of data on a hard drive is based on five numerical values.

• Cylinders

• Heads

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• Landing Zone

• Sectors

• Write Precomp

Write Precomp and Landing Zone are obsolete, but are often seen on older drives.

Knowledge of the physical layout of data is required in order to properly install and configure a hard drive. The BIOS needs to know how to find the data. If you look at any documentation that comes with a new hard drive, you will find information regarding the cylinders, heads and sectors. These values are commonly called CHS values (Cylinders, Heads, Sectors). Also, many drives will have this information printed on the label.

The following is an example of the documentation for a Seagate drive.

Addressing Cylinders Heads Sectors

ST31720A

LBA addressing 826 64 63

CHS addressing 3,305 16 63

Note. This drive does not use the write precomp or landing zone parameters. Set these parameters to zero.

Note: LBA and CHS addressing will be covered further in this section.

Now let’s look at the individual components and see how they affect storing data.

Cylinders

Data is stored in concentric circles on the surface of each platter. Each concentric circle is called a track. A set of tracks (all tracks of the same diameter) through a stack of heads, is called a “cylinder.” The number of cylinders is the logical number used to describe the drive (not the number of tracks). BIOS limitations set the maximum number of cylinders (for calculation purposes) to 1024.

Cylinders

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Heads

We have already talked about hard drives containing one or more platters. Each side of a platter is considered a head. Therefore, the number of heads equals the total number of sides of all the platters used to store data. If a hard drive has 6 platters, it could have up to 12 heads. Hard drives using voice coil motors for actuator arms must reserve a head for navigation (accuracy of the arm position). Since platters are two sided it is logical to always have an even number of heads. However, if one is used for navigation, the reported number of heads will be an odd number. Again, the BIOS limitations set the maximum number of heads to 16 (for calculation purposes).

Drive Heads

Remember, CHS numbers are logical values. This has allowed some hard drive manufacturers to use a technology called sector translation to create more than one logical head on a single side of a platter. Sector translation is a software conversion of the actual values into values that the BIOS will accept. Regardless of the methods used to manufacture a hard drive, BIOS limits the maximum number of heads (for calculation purposes) to 16.

Landing Zone

As we mentioned, early drives using stepper motors required a place to park the heads when the drive is not running. A landing zone designates one cylinder for safely parking the read/write heads. A landing zone is only used on older drives that have stepper motors to drive their actuator arms.

Sectors

The third element of CHS values is Sectors. A hard drive is cut (figuratively) into small arcs (like a pie). Each arc is called a sector, and holds 512 bytes of data. Each sector will contain, in addition to the data, header information that includes the sector ID or number and trailer information that includes a checksum to insure data integrity. As with the other CHS values, the BIOS sets a limit on this one too. BIOS limitations set the number of sectors at 63.

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Sector

Write Precomp

If you look at the graphic of a sector or a slice of pie, it is obvious that the outside regions are larger than the inside regions. This is the same with sectors; the outside ones are physically larger than the inside ones. Since all sectors can logically store only 512 bytes of data, the ones on the outside have space left over while the ones on the inside are cramped. The technology of early drives needed a method of compensating for this anomaly. This method was called “write-precomp.” It literally means a point (the cylinder) at which the drive needs to compensate for the size difference of sectors. As we saw in our example of the Seagate drive, write precomp is no longer used.

Calculating the Size of a Drive

When installing a hard drive, it is important that you provide the computer’s BIOS the information it needs to recognize the drive so that it can address all the sectors that contain data. If the computer does not know these values or has the wrong values, it will not recognize the drive. Once you know the three CHS values of a drive, you can calculate the capacity.

Cylinders Heads Sector

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Lets look at calculating the maximum hard drive size when considering the BIOS limitation of CHS. The BIOS limits are:

1024 cylinders

16 heads

63 sectors

512 bytes per sector

Therefore:

1024 x 16 x 63 x 512 bytes/sector = 528,482,304 bytes

This value can be rounded to 528 megabytes or if you divide the total number of megabytes (1024 x1024 or 1,048,576) into the total number of bytes, you will get 504 MB. Keep these two numbers in mind as they are often used interchangeably.

Based on these values, the largest hard drive size recognized by the BIOS is 504 MB.

Today’s standard drives far exceed these early limits. In fact, it would be difficult to find a computer with less than a 2 GB hard drive. However, as a computer technician, you may encounter one of these older drives. Larger drives manage to exceed this limitation in two different ways. We mentioned sector translation as a method of converting logical values into values that the BIOS can understand. Other translation methods can be employed that allow the BIOS, the CPU and the drive controller to report and see the CHS values that they need to run. The other method is to replace the BIOS. (More on this to follow).

Hard Drive Types

If you purchased one of the original personal computers, you will remember that hard drives were not included. As hard drives were introduced into the personal computer market, a large variety of drives became available, each with their own CHS values. To simplify installation, IBM created standard “types” of drives. To configure a drive, all the technician had to do was enter the drive number into the BIOS setup. The correct CHS values would then be properly configured. This system worked for some time, but as increasingly drives entered the market, increasingly drive types had to be added to the list. This created an additional problem in that BIOS’s were outdated because they did not contain the latest list of types. So, at type 46, the decision was made to stop adding new types and use type 47 as “User”. From this point on, the BIOS did not need to be updated, but the technician had to select type 47 and manually configure the CHS value.

Today, the process is even more simplified. A 48th type has been assigned. That type is ”Auto”. With auto, the BIOS information is stored on the hard drive itself. When running the BIOS setup, a ROM chip on the hard drive will be queried and the following data collected:

• Buffer type indicating sector buffering or caching capabilities.

• Cylinders in the current translation mode.

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• Cylinders in the default translation mode.

• Drive manufacturer.

• Drive model and serial numbers.

• Firmware revision number.

• Heads in the current translation mode.

• Heads in the default translation mode.

• Sectors per track in the current translation mode.

• Sectors per track in the default translation mode.

While this is simple, as an A+ technician, you will need to be familiar with all three methods of configuring BIOS for a hard drive. Those methods are:

Enter the drive type number.

Use type 47 “USER” and enter the values manually.

Use the auto function and let the BIOS collect the information from the drive.

Hard Drive Interfaces

The development of hard drives followed two paths. The first and most obvious was to be able to store more and more data in a smaller and smaller place. This growth was based on the technology of the read/write heads and how accurately information could be stored and retrieved. The second path was around the interface. A hard drive interface is the standard that determines how the drive communicates with the motherboard and CPU. In fact, hard drives are actually categorized by the interface. Let's look at hard drive interface technology as it progressed from the early drives to today’s behemoths. With each new interface came many advantages. As a computer technician, you will have to know these differences.

ST506/412

Seagate introduced their ST-506/412 drive in 1983. This drive required that the ROM BIOS chip be installed on the controller that was a separate component at that time. These full-height 5-¼ inch drives have taken their place in the annals of computer history books alongside the Hollerith card. It was not until the introduction of the AT system that the BIOS was placed on the motherboard. These drives are easily identified, as unlike hard drives of today, these drives require a separate cable for data (20-pin) and the controller (34-pin). In addition, like its predecessor the floppy drive, the controller cable could connect to two drives and uses a twist to select between the two different drives.

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ESDI

The first attempt at hard drives produced a workable, but low performance mode. It became obvious very early that hard drives were here to stay and performance improvements would be required. In 1983, the Maxtor Corporation introduced the next generation hard drive. This drive was called ESDI or Enhanced Small Device Interface. Performance enhancement was achieved by integrating the controller functions directly onto the hard drive itself. This approach greatly improved data transfer speeds. In addition to the controller, some ESDI controllers offered enhanced command sets. One of the features of the new command set was to support auto sensing of the drives.

The installation of ESDI drives was no problem as it is almost identical to the installation of ST-506 drives. As with their cousin the ST-506/412, these drives are now part of computer history.

IDE

The replacement to the ESDI came on scene in the early 1990s. This new drive was called the IDE or Integrated Drive Electronics (pronounced Eye-Dee-E). The name IDE is derived from the fact that the drive has a built-in (integrated) drive controller. These drives incorporated the benefits of both of its predecessors. IDE quickly became the standard for hard drives in personal computers.

The installation of the original IDE was quite different from its predecessors. These drives were designed as part of an expansion card and were installed into a free 16-bit ISA slot on the motherboard. Because of this, they were often called hardcards. From these first hardcards was developed what is now considered the standard 40-pin connector on motherboards. These connectors are actually a compressed version of the standard 98-pin standard 16-bit ISA bus slot. The reduction of pins is simple because all the pins not used by the controller were simply eliminated. Western Digital and Compaq developed the first ATA IDE drives and were the first to establish the 40-pin IDE connector specification that is now standard in all computers. ANSI standards committees accepted the standards as the Common Access Method (CAM) AT. The official name for these drives is now ATA/CAM (AT Attachment/Common Access Method). The terms IDE and ATA/CAM are often used interchangeably. With this standard, drives started using a single cable with no twist. Since two drives can be connected to one cable, each drive must be individually configured as either a master or a slave. Some drives have stand-alone and auto configuration as well. Switches or jumpers on the drive are used to complete the configuration. This is now a standard method for installing drives.

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ATA

ATA is an implementation that integrates a controller right on the disk drive making the device more intelligent. It functions as the “go-between” for data transfer. ATA can transfer data up to 6.67 MBps or if utilizing a cache-hit burst, up to 10 MBps. It is somewhat limited in its ability to attach devices. It can only handle two channels with two drives per channel. This particular implementation is the common one, especially for off the shelf units.

This version is also known as IDE. It has a 16-bit interface and can support up to two hard drives as well as PIO (Programmed Input/Output) modes 0, 1, and 2.

ATA-2 (Fast ATA/Enhanced IDE [EIDE])

This version supports multiword DMA modes 1 and 2. It supports PIO modes 3 and 4, which are faster than PIO modes 0, 1, or 2. It also supports LBA (Large Block Addressing).

ATA-3

This version held little change from ATA-2, but it introduced SMART (Self-Monitoring Analysis and Reporting Technology).

ATA-4 (Ultra-DMA/ATA-33/DMA 33)

This versions supports multiword DMA mode 3, which runs at 33 MBps. It also introduced CRC (Cyclic Redundancy Check) error checking.

ATA-5 (ATA/66 / Ultra DMA/66 / Fast ATA-2)

This version doubles the throughput to reach 66 MBps, because it doubles the burst rate of ATA-33. This helps with data-transfer bottlenecks. It also uses CRC (Cyclic Redundancy Check) error checking. It uses a 40-pin cable connector.

Ultra-ATA 100 (Ultra ATA DMA Mode 5)

This version has a maximum data transfer rate of 100 MBps. It also uses CRC (Cyclic Redundancy Check) error checking.

EIDE

The logical successor to the very popular IDE or ATA drive is today’s standard known as the Enhanced IDE (EIDE). It is also called ATA-2 and ATA-3. It has several improvements.

• Increased drive capacity.

• Increased speed for data transfer.

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• A secondary channel, which allows support for up to four devices.

• ATAPI (AT Attachment Packet Interface) to support non-hard drive storage devices such as CD-ROM drives.

The details of how EIDE increased hard drive capacities and transfer speeds will be covered later in this section (Programmed I/O and DMA). The other two improvements really made a difference in how we perceive our computers today. The original controllers allowed for only hard drives (and only two of them). As we have seen, these drives are connected on the same cable. The addition of two channels (two cables) allows a computer to be expanded further, allowing four drives to be added. This allows the computer’s storage capacity to be physically expanded. This capability was further enhanced with the acceptance of the ATAPI (AT Attachment Packet Interface). The interface was developed by an independent industry group to allow non-hard drives (CD-ROMs and high-speed streaming tape units) access to the ATA interface. Now almost every computer sold has a standard CD-ROM installed on the second IDE channel for their motherboard.

SCSI

The Small Computer System Interface (pronounced - scuzzy) is considered a high-end hard drive by many. In reality, this is a misnomer. SCSI is not a disk drive, but a bus interface. The SCSI bus provides a communication path between the SCSI device controller and the computer’s system bus. Using a SCSI bus, up to eight peripheral devices can be daisy-chained (seven devices and a host adapter). It just happens, that the most popular use of a SCSI bus if for hard drives. SCSI will be discussed in more detail later in this chapter.

Installation and Set-Up of a Hard Drive

All boot devices must be configured outside of the operating system (DOS – Windows 9x – Windows NT – Windows 2000) regardless of the level of plug n’ play compatibility. Devices that are used to boot must be configured at the BIOS and hardware level since they typically contain the operating system and must run properly before the operating systems can be started.

Installation Procedure

Installation of a hard drive is simple and requires five steps:

• Physical Installation and Cabling

• CMOS Setup

• Low-Level Format (if required)

• Partitioning

• High-Level Formatting

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Physical Installation

The most important consideration when installing any drive is to correctly install the cabling. The figure below shows a standard IDE drive. Note the alignment of pin number 1 and the power connector.

IDE Connections

Unlike the twisted cable provided with floppy drives to identify one drive from the other, hard drives use a flat cable with no twist. Therefore, each drive must be designated as either the master or slave so that the BIOS can identify them on the cable. The documentation supplied with the drive should provide the necessary information for configuration. Often this information is printed on the label on the drive. Both drives must be properly configured before starting the system. If the drives are not properly jumpered, they won’t work. This is a very important concept for the A+ Exam!

There are two different drive-naming conventions. The one we are most familiar with is the A:, B:, C:, D:, etc. These names apply to how the drive is formatted, how it is seen by the operating system and its cable orientation. At this point, we are not interested in these names; we are still working at the hardware level where the drives are numbers. If only one hard drive is installed, it must be configured as drive 0 or Master. A second drive on the same cable is installed as hard drive 1 or Slave. If you use two controllers with two cables and four drives, each controller will have a master and a slave. One controller will be designated as the primary controller and one as the secondary controller. A single drive installed on a computer must therefore be connected to the primary controller and designated as the master or drive 0.

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Master/Slave Jumper Settings

CMOS and Hard Drives

After physically installing a hard drive, the geometry of the hard drive must be entered into the CMOS through the CMOS setup. This information must be exactly as specified by the manufacturer.

Hard drive configuration information in a typical CMOS

CMOS Main Screen

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Sub Screen of Main - Hard Drive Set-up Screen

Hard Drive Set-up Screen

Originally, CMOS would only allow settings for two drives. Later versions allow up to four drives.

CMOS setup is easy with IDE drives. As mentioned earlier, new drives contain their own BIOS information. By using auto-detection, from the setup program, the correct information is read from the drive and stored in the CMOS chip. Be sure to SAVE with EXIT!

Tip: If a CMOS with the IDE Autodetect feature is not available, there are utility programs available that will read the geometry of a hard drive. The data still has to be entered into the CMOS. If you can detect the drive using the Autodetect feature, you have the drive installed properly.

What happens if the wrong data is entered into CMOS? For example, a 1.2 GB hard drive is installed and the CMOS was setup to make it a 504 MB hard drive. When you boot the computer, you will see a perfect 504 MB hard drive.

The CMOS can be reset back to the proper settings, but all the data on the drive will be lost! Be careful and always keep a backup copy of your CMOS information.

There are many ways to determine the geometry of a hard drive.

• The best source of information is the hard drive itself and the documentation that came with it. Check the label on the drive or contact the manufacturer. Many manufacturers have a toll free number. Also, try the Internet.

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• If you cannot contact the manufacturer directly, try a third-party source. There are many books dedicated only to the details of hard drives. These will often have an appendix full of tables with common hard drive configurations. You can also try sources such as the Micro House Technical Library. The MicroHouse Technical Library is an outstanding resource for any technician and provides detailed information on thousands of hardware components.

Low-Level Formatting

Low-level formatting creates all the sectors, tracks, cylinders, and head information on the drive. It also creates the intersector and intertrack gaps and records the sector header and trailer information. As a computer technician, you do not have to worry about low-level formatting. For the most part, it is done at the manufacturing level so you will not be required to do it. Only on a rare occasion, you may run into a problem with an older drive and you may have to run a low-level format. You will need to obtain the correct software and instructions from the manufacturer. Floppy disks will need low-level formatting, but it is included as part of the high-level format.

Bootable Disk

Once you have a correctly installed and operational hard drive you will need to have a bootable floppy disk to complete the installation. A bootable disk contains all the necessary files to boot a computer. You will also have to copy some DOS files that will allow you to complete the installation of a hard drive. There are two ways to create a bootable disk depending on whether or not you are using DOS or Windows 9x.

To make a bootable disk from DOS, insert a floppy disk into the A: drive. From the command prompt, type: FORMAT A: /S. This will prepare the floppy to be bootable by copying system files to the diskette. Now you will need to copy two files from the C:\DOS> directory. These files are:

• FORMAT.COM (or FORMAT.EXE)

• FDISK.COM

Note: With Windows 9x O/S, the DOS commands are found in C:\WINDOWS\COMMAND directory).

In Windows 9x, a boot disk is also called a startup disk. If you open the Add/Remove Programs icon in the control panel, you will find a tab called startup disk. By selecting the create button and following the instructions you will create a start-up disk with all the necessary files.

You can now use this bootable disk to start a computer from the floppy drive and to complete a hard drive installation by partitioning and high-level formatting.

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Creating a Start Up Disk in Windows 98

Partitioning

Partitioning is used to divide a physical hard drive into logical units. You will need at least one partition on every drive, but you may want to create more. If you intend to use the drive with more than one operating system such as Windows 98 and Windows NT, you will need a separate partition for each. They are not compatible. In addition, if you have a large hard drive (larger than your system will support), you can divide the drive into smaller logical units. Your system will see each of the smaller units, thus allowing you to use the entire drive. First, let us consider our choices for file systems. Each is based on how files are stored and indexed for retrieval.

FAT (File Allocation Table – also known as FAT16) – This is the standard file system for DOS. Subsequently, Windows 3.1, Windows 9x, Windows NT, and Windows 2000 will run on a FAT 16 drive. FAT uses 12 (floppy disk) and 16 (hard disk) bit numbers to identify clusters. Clusters are groups of sectors. By grouping sectors into clusters, drives as large as 2 gigabytes can be recognized. More on clusters in the following section. You can only create two FAT partitions on a single drive. One is the primary and the other is the extended. The extended partition can be further divided into as many a 23 logical drives (D-Z). When a file is stored, it is broken up into smaller units and distributed through as many sectors as needed. The FAT table is simply an index that keeps track of which part of the file is stored in which sector.

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FAT32 – This is a relatively new system supported by Windows 95 OSR2, Windows 98 and Windows 2000 (Windows NT 5.0). This system uses 32-bit numbers to identify clusters, which results in a maximum volume size of 2 terabytes (a terabytes is a gigabyte times 1024 or 1024 x1024 x 1024 x1024 bytes).

Note: Windows NT 4.0 will run on FAT16 but not on FAT32

Since FAT32 is new you may have to make a choice when to use it and when not to use it. Here are some suggestions:

• Don’t use FAT32 on any partition that other operating systems will use, except Windows 95 OSR2.

• MS-DOS, Windows 3.x, the original release of Windows 95, and Windows NT clients can’t read FAT32 partitions shared across a network.

• If you dual boot between Windows 98 and another operating system (such as Windows NT 4.x) the drive C: partition cannot be FAT32.

• You cannot compress FAT32 partitions.

• Windows 98 MS-DOS mode fully supports FAT32, so you can run most MS-DOS mode games and applications from FAT32 partitions.

• Some older applications written to the FAT16 specification may not display disk space larger than 2GB.

• Do not use any utilities that do not support FAT32. This may result in data loss and may corrupt the file system on the hard drive.

NTFS (Windows NT File System) - This is the native file system for Windows NT. It will support up to 16 exabytes (an exabyte is a terabyte times 1024). This file system also supports many advanced security features that are applicable to networking operations.

How the File Allocation Table Works

A File allocation table is an index that keeps track of two pieces of information. The first is the cluster ID that is a hex number that identifies the location of the cluster. The second piece of information is a status code.

When a file is saved - DOS starts at the beginning of the FAT, looks for the first empty cluster, and begins to write the data. Once the cluster is full, (512 bytes) it will enter the location of the next open cluster in the status field for that cluster and continue to write data. After all the data is written, it will use the code FFFF to indicate that this is the end of the file. This creates a map from cluster to cluster identifying all the clusters that contain a specific file.

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Note: If you ever see the error “lost cluster” it simply means that one of the code fields points to the wrong cluster.

One of the anomalies of this type of file storage is fragmentation. Fragmentation is the scattering of files all over the drive. As a file is written to sectors (clusters), it is placed in the first available location. As files are deleted an opening occurs, and they are filled with the next file to be saved. With time, this process will begin to scatter files all over the drive. This is an acceptable way to operate and causes no problems for the computer. However, it slows down the hard drive since it has to access two or more places to retrieve a file. It is possible for a file to be fragmented into hundreds of pieces; forcing the read/write heads to travel all over the hard drive to retrieve a single file. The elimination of fragmentation will improve the speed of the hard drive dramatically. The details of defragmentation are covered later in this chapter under “Maintaining a Hard Drive”.

Sectors and Clusters

Before we get back to partitioning, we must first understand the term clusters. As we have seen, the CHS values limit the maximum size of a hard drive to 504 MB. Since FAT uses a 16-bit binary number to identify locations, it can address 2l6 or 65,536 locations. To round this off, divide by 1024 bytes per kilobyte and you get 64K. Therefore, the size of a hard drive partition should be limited to 64K x 512 bytes/sector or 32 Megs. With this limitation, how are larger hard drives used?

There are two answers to this problem. The first method, used with earlier drives (under 100 Meg), was to use partitioning to break the drive up into multiple partitions, each being less than 32 Megs.

The second method is called Clustering. Clustering involves combining of a set of adjacent sectors into one logical unit. The logical unit being called a cluster or group of sectors. The number of sectors in each cluster is determined by the size of the partition, since there can never be more than 64k clusters. To determine the number of sectors in a partition, divide the number of bytes in the partition by 512 (bytes per sector). Then divide the number of sectors by 64,000 (maximum allowable clusters). The following table shows how this works.

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Estimate of Sectors/Cluster

Partition MEG

Total Bytes Total Sectors Sector/Cluster Byte/Cluster

32 33,554,432 65,536 1 524

64 67,108,864 131,072 2 1,049

128 134,217,728 262,144 4 2,097

256 268,435,456 524,288 8 4,194

512 536,870,912 1,048,576 16 8,389

1,000 1,048,576,000 2,048,000 32 16,384

2,000 2,097,152,000 4,096,000 64 32,768

4,000 4,194,304,000 8,192,000 128 65,536

Naming of Partitions

The main reason for partitioning came about because of limits imposed by DOS. As drive technology exceeded the development of DOS, it was necessary to have a means of recognizing larger and larger drives. DOS could only recognize up to 32 Megabytes of a drive. With the release of DOS 3.3 and partitioning, a drive could be sub-divided into logical units small enough for DOS to handle. With time, and improvements in DOS, larger partitions could be recognized but the practice of naming the partitions stayed the same. As stated earlier, a DOS drive can have only two partitions, a primary and an extended.

A PRIMARY partition is a bootable partition. This is where the operating system is stored. When a computer boots from a hard drive, it looks for a special sector in the primary partition called the Boot Sector. This sector will tell it where the operating system is located and how to get started. The name of the Primary partition is “C:”

The EXTENDED partition is for the rest of the hard drive. The extended partition can be one drive or be logically partitioned into several drives. Each of the drives will be assigned a drive letter starting with the letter “D:” and progressing until drive letter “Z:” is created (remember, “A:” and “B:” are reserved for floppy disk drives).

Note: if your boot sector is corrupted or erased, your computer won’t find an operating system.

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Examples of Partitions

One 500 Meg Physical Drive with 1 Partition

C: (Primary Drive)

One Physical Drive - One Logical Drive

One 1.0 Gig Physical Drive with 2 Partitions

C: (400 Meg Primary Drive)

D: (600 Meg Extended Drive)

One Physical Drive - Two Logical Drives

One 4.3Gig Physical Drive with 3 Partitions

C: (1.0 Gig Primary Drive)

D: (1.65 Gig Extended Drive)

E: (1.65 Gig Extended Drive)

One Physical Drive - Three Logical Drives

How to Partition a Hard Drive

The FDISK utility is used to partition a drive. After the drive is installed and CMOS is updated, run FDISK to partition the drive(s).

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MSDOS FDISK Start up screen

The function of lines 1, 3 and 4 are clear. Line 2 sets the active partition. The active partition is the partition where the BIOS will look for an operating system when the computer is booted.

Don’t confuse primary partition with the active partition. On a computer with a single operating system, the primary and active partition is normally the same partition. A computer with dual-boot capability may have separate partitions for each operating system. In this case, the active and primary partitions may not be the same.

The primary partition is where DOS is stored on the hard drive and the active partition is where the operating system is stored on the hard drive. Other operating systems can exist on an extended partition. If DOS is on the primary partition, and another operating system is on an extended partition, there must be a mechanism to switch the active partition to the operating system’s partition.

Advanced operating systems can create a special partition called a “boot partition.” The boot partition is set to active. When the computer boots, a menu appears which prompts the user to pick which operating system to use. The boot manager then sets the chosen partition as active which starts the operating system located in that partition.

DOS must be placed on the primary partition (the C: drive). If there are two operating systems and one of them is DOS, DOS must be on drive C:, OS/2, UNIX, and Windows NT can all boot from another drive letter as well as from the C: drive.

Note: if you attempt to format a hard drive before creating a partition, you will get the following error message: “invalid media type”.

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High-Level Formatting

The final step in installing a hard drive is to format the drive. The DOS command FORMAT will perform both low-level and high-level formatting on a floppy disk, but only perform the high-level format on a hard disk. Low-level formatting for IDE and SCSI drives is performed by the manufacturer. During formatting, the operating system writes the structures for managing data and files on the hard disk. This does not physically alter the drive, but creates a table of contents for the disk. It creates two copies of the file allocation tables (FATs) and a volume boot sector. Formatting is operating system specific. If you format a disk for use on the Macintosh operating system, you will not be able to access it from a computer running a DOS format.

Maintaining a Hard Drive

Hard drives are very rugged devices and from a mechanical perspective either work or don’t work. They are completely enclosed and have no user serviceable parts. In fact, if you attempt to open them you will damage them and certainly destroy the drive. The only practical way to repair a drive that has suffered a mechanical failure is to replace it.

The problem of maintaining a hard drive really revolves around protecting yourself from loss of data and at least being able to recover the data if possible. Being prepared before a hard drive fails can save lost data and time. How prepared you need to be depends on two things.

• How much can you afford to lose?

• How much time do you have to start over?

With this in mind you can minimize the impact of a hard drive failure by performing good and regular backups, being sure to save a copy of the Boot Sector and Partition table. Loss of the boot sector or partition table will prevent you from accessing the data. There is no worse feeling than to know that your data is intact, but you cannot access it. Restoring the boot sector and partition table can often get your data back. Several third party software packages will do this for you. Just remember that you will have to save this information before you crash. Don’t forget to maintain your fan(s) to maximize airflow and keep temperatures down.

Microsoft to the Rescue

A long time ago, Microsoft recognized the need for some form of disk maintenance. To help maintain hard drives, two programs are included as part of their operating system. These programs are Defrag and ScanDisk.

If you recall from the earlier section on fragmentation, the process of saving, deleting and saving new files can cause data to be scattered all over the drive. The method most commonly used to remedy this problem is running a program to eliminate fragmentation. This is called “defragmenting” a drive. There are several programs designed to defragment hard drives, including DOS’s DEFRAG and NORTON UTILITIES’

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SPEEDDISK. Windows 9x includes its own version of a Defragmentation program. It is called Disk Defragmentor and is located in the Start | Programs | Accessories | System Tools menu.

NOTE: DEFRAG cannot re-write or move system and hidden files. These files may be program files that are copy protected and must not be moved after the program is installed. System files, such as the DOS Core Program, must occupy a particular position on the disk.

Warning - never run a defragmentation program designed to run in DOS or Windows 3.x on a Windows 9x system. It may not understand the Windows 9x long file names and data may be lost.

DOS, Windows 3.x and Windows 9x contain versions of the ScanDisk program. ScanDisk performs a battery of tests on a hard disk, including looking for invalid filenames, invalid file dates and times, bad sectors and invalid compression structures. In the file system, ScanDisk looks for lost clusters, invalid clusters and cross-linked clusters. Regular use of ScanDisk can help prevent problems as well as resolve them. Windows 9x-based computers will automatically run ScanDisk any time the operating system is improperly shut down (when the power is turned OFF before the system is allowed to complete its shut down procedures). ScanDisk is not perfect, and probably won’t recover a badly damaged drive. However, it will (when used frequently) find lost clusters and bad sectors. Lost clusters can be recovered by converting them to individual text files. You will then have to manually open each of the files and reassemble them. Any bad sectors can be Xed out so that no good data will be put into them.

While these two tools are not a surefire cure for hard drive problems, regular use of them can prevent many failures and increase the performance of a computer. Microsoft is so confident in this that the Windows 98 operating system has a scheduler program that will allow you to schedule maintenance (Defrag and ScanDisk) for off hours.

When all else fails

When a drive goes bad and you have expended all efforts to recover your data you have only two choices left. The first is to start over. This means to re-partition and re-format the drive. It is possible that this procedure will reactivate the drive, however, all data will be lost. The second is to replace the drive. With the cost of drives falling every day, the money you spend on sending the drive out to be remanufactured or rebuilt will most likely be more than the cost of a drive that will hold 2 or 3 times the data.

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Hard Drive Problems

Hard drive problems are no different than the ones encountered with floppy drives. The primary difference is that the errors will read “HDD” instead of “FDD”. Just like troubleshooting a floppy, check the following:

• The cables and connections

• BIOS/CMOS

• The drive

• The controller

High Capacity Hard Drives

So far, our discussion has been limited to what is considered a standard drive. These drives are less than 1-gigabyte. Typically, larger drives could be employed, but required that the drive be partitioned in units of 528 MB or less. Today, a standard drive is 20 gigabytes with sizes easily exceeding 40 gigabytes available. These early drives were relatively simple to install as they were handled by the system BIOS. They used the routines built into the original IBM AT and the same interface command set as the original ST-506 hard drive. As drive capacities grew, they required many changes in setup to allow circumvention of the limitations imposed by earlier models.

Limitations of Early Drives

The limits to hard drive sizes were imposed by the limits of the BIOS and the ATA specifications. Early BIOS had a limitation on the maximum CHS values allowed. In addition, the ATA/IDE standard had its own limits. Independently, these each could support large drive capacities, but the combining of these two requires taking the lower of the two; therefore, the maximum hard drive size was limited to 528 MB. The following table shows how CHS limits are determined.

CHS Limits

Cylinders Heads Sectors

BIOS Limit 1024 255 63

ATA (IDE) Limit 65536 16 255

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Choosing the lowest from each category and calculating the size, you will get the maximum size allowed (remember there are 512 bytes per sector).

1024 x 16 x 63 x 512 = 528,482,304

This number is displayed in one of two ways. As either 528 megabytes (simply rounding off the number) or 504 MB which is the short hand version. The 504MB is derived by dividing 528,482,304 by 1,048,576 (the number of bytes in a MB).

Increasing Capacity

One method to circumvent these limits is to use an advance BIOS. These BIOS use what is known as translation. Translation works in between the BIOS and ATA/IDE standard. It lies. It will report a different geometry when talking to the drive and when talking to the software. This way, both are happy and we get to use larger drives. You can tell if you have enhanced BIOS by looking at the setup utility. If you can specify larger than normal settings, you most likely have an enhanced BIOS. There are three ways that BIOS can handle translation; Standard CHS, Extended CHS and LBA.

In a standard CHS, the geometries printed on the label of the drive are the logical values. All translation is accomplished internally on the drive. In extended CHS, the translation takes place both at the drive and the BIOS. One translation is used when communicating between the drive and the BIOS and another when communicating between the BIOS and everything else. Extended translation is also called “Large” or “ECHS” in a BIOS setup. On the A+ exam, it may be referred to as Large LBA.

Logical Block Addressing (LBA mode) means linearly addressing sector addresses. A 28-bit binary number is used to assign a number to each sector starting with 0 and going as high as 268,435,456. Every sector on the drive then has a unique number. With 512 bytes per sector, LBA will translate drives up to 137 billion bytes (128GB). While this solves one side of the equation, the BIOS still limits the maximum capacity to about 8GB (1024 cylinders, 256 heads and 63 sectors).

Before (limit 528)

Capacity = Cylinders x Heads x Sectors

528,482,304 = 1024 x 16 x 63 x 512

With LBA

Capacity = Cylinders x Heads x Sectors

8,455,716,864= 1024 x 256 x 63 x 512

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Increasing Data Transfer Speeds

In addition to larger storage capacities, new drives employ two methods of increasing the speed at which data is transferred. These are Programmed I/O and DMA transfer.

With the release of the ATA-2/EIDE specifications, came several modes for high-speed data transfer. When installing a drive, you will want to be sure to run at as high a speed as the system can support. These modes are called PI/O or just PIO. Programmed I/O is based on a speed of 16-bits being transferred in 600 nanoseconds (ns) or one cycle. The following table shows the transfer speed for Programmed I/O 0 through Programmed I/O 4.

Programmed I/O Transfer Speeds

Mode Cycle Time (ns)

Transfer Rate (MB/sec)

ATA Specification

0 600 3.33 1

1 383 5.22 1

2 240 8.33 1

3 180 11.11 2

4 120 16.67 2

A second method of transferring data will move data directly from the drive to memory. This method is called Direct Memory Access (DMA). The big difference between Programmed I/O and DMA is that DMA does not access the CPU. DMA will rely on a DMA controller on the system motherboard to control the data transfer. Any device using DMA must be assigned a DMA channel and no two devices can use the same channel. DMA can also operate using bus mastering. In bus mastering, a controller on the device will take control of the computer’s bus while the CPU is not using it.

Installing EIDE Drives

Physical installation of EIDE is the same as its predecessor the IDE. As we have learned, a few more settings must be made to insure maximum performance.

Enable Secondary Controllers

Now that we have the ability to install up to four devices, we will need to be sure that our controllers are setup properly. First, we must make sure that both the primary and secondary IDE controllers are enabled. You will need to check the CMOS setup utility and perhaps the motherboard documentation. Look for any jumpers or switches that may enable or disable the secondary controller. If the computer is using an expansion card

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instead of connecting directly to the motherboard, you will have to inspect it for any jumpers also. Don’t forget to set the master/slave setting on the drive. Each IDE controller can have one master and one slave. If for example, you have two drives and elect to install one on the primary and one on the secondary, they will both be set as master.

Set the Enhanced BIOS

During your BIOS setup (CMOS setup), be sure to set the correct BIOS settings to handle translation: Standard CHS, Extended CHS and LBA. Some computers do not support extended CHS or LBA, but you may be able to use them anyway. These drives are usually provided with a special software disk called a Dynamic Drive Overlay (DDO). When installed and enabled, this software adds another layer of translation between the BIOS and the operating system. While this will provide a solution, it does have some problems. The most important is that this software must always run before the operating system. If for example, you boot a computer that used DDO from a standard system floppy, you will not be able to see the drive. You must boot from a special boot disk that will run the DDO first. Fortunately, with the new computers, there is very little need for these drivers anymore, but you should be aware of them just in case.

Setting Programmed I/O Mode

You must properly set the Programmed I/O mode. The best performance of the system will be based on the performance of the slowest device. Therefore, check the Programmed I/O of the drive, the controller and the BIOS. Programmed I/O settings are made through the BIOS setup utility.

SCSI Drives

SCSI (Small Computer Systems Interface) has become the mass storage device of choice for large network installations requiring some level of fault tolerance. They are also the interface of choice for systems requiring storage of large amounts of data, such as in the imaging industry. While SCSI has many advantages over standard IDE and EIDE drives it has only one reported disadvantage that has limited its use in the personal computer industry. That disadvantage is its cost. In many installations, the advantages far outweigh the cost. Some computer manufacturers such as mainframes and Macintosh have recognized the advantages and based their systems entirely on the use of SCSI. SCSI was Macintosh’s answer to expandability, as their early computers did not have an expansion bus like their PC counterparts. In scenarios where speed and reliability are first, choose SCSI. On the other hand, if cost is first, look at IDE and EIDE.

Shugart Associates introduced SCSI as a systems interface in 1979. When we look at SCSI, the first inclination is to identify a SCSI device as a SCSI hard drive. In fact, SCSI is not a drive, but an interface. Moreover, not just a drive interface, but a systems interface. SCSI consists of a host adapter or I/O interface, and up to seven other devices. These devices can include hard drives, tape drives, and CD-ROM drives, just to name a few. SCSI acts like an independent bus that communicates with the CPU through its adapter or interface. All eight devices (seven devices plus the host adapter) are

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connected together in a chain. SCSI devices can be internal devices or external devices. The only difference between the two is that external devices will require an external power source while an internal device will derive its power from the computer’s power supply.

A SCSI chain is a group of SCSI devices connected together in a series. Typically, each device will have two connectors, one for each device next to it. The host adapter (usually a card) can be located anywhere along the chain and makes the connection to the computer through the external data bus. The following figure shows a SCSI chain with two internal hard drives and an external tape backup and CD-ROM.

SCSI Chain

Installing SCSI

Installing a SCSI device is physically the same as installing any other device. You will need to install the hardware, connect any cables and then install any necessary software drivers. There is one big difference. That is, if improperly connected, you are risking damage to the device. Remember, installing an IDE cable backwards will only cause the device to not run; installing a SCSI cable wrong can damage the device.

Another difference is that you are installing a bus or chain of drives. You must install a controller card that will need to be properly configured to the computer. This includes any address and interrupt (IRQ) information. After that, you must configure each device to its SCSI chain. As long as you follow a few simple rules, you will have no problems.

Note: Some SCSI today is plug-n-play compatible and so it will take care of these for you, but as a computer technician, you must be able to configure devices on your own. Also, be aware that SCSI tape drives might require special attention, such as enabling int13h support.

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Rule #1 – Terminate

SCSI chains are considered a bus because they function like buses. However, they are actually more like a network bus. The signals that are used are not simply ON and OFF; they are more like radio signals. When transmitting a signal of this type, it will literally move down the wire in both directions until it gets to the end. When it gets there, it has no place to go so it will reflect back down the wire in the opposite direction. This reflection or echo will corrupt the signal that is following it and cause the system to fail. To prevent this corruption, the signal must be absorbed. To absorb the signal, we install a termination resistor at each end of the cable. Terminating resistors are considered passive devices and operate at 132 ohms.

Proper termination of a SCSI device requires special consideration. Failure to properly terminate can damage the hardware. On most of the devices within a computer, the appropriate termination is built-in. On other devices, including SCSI chains and some network cables, termination must be set during installation. The only rule is that BOTH ends of the chain must be terminated.

Methods of Terminating:

• Plug in termination resistors - these can come in several forms. One method is to provide a cable connector with the resistor built-in. These are installed on the second cable port. Another method is to provide an actual resistor that must be inserted into the proper connection.

• Jumper and switch settings - many devices provide either a set of jumpers or switches that are used to enable or disable the terminators.

• Auto detection - some devices will detect that they are on the end of the SCSI chain and will automatically terminate themselves. (Do not make this assumption.)

• Software termination - advanced host adapters will provide termination through software.

Warning! Proper termination is serious business.

Rule # 2 – Set the ID

A simple SCSI chain works like a network and just like a network, each device requires its own unique address. Unlike a network, this is a very simple process. Each device requires a unique ID number between 0 and 7. The only hard and fast rule is that no two devices on a drive can have the same ID number.

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SCSI numbering conventions:

• Host ID is set to 7. This is not a requirement, more of a de-facto standard.

• The placement of devices on the SCSI chain has no bearing on the ID number. They do not have to be in any particular order.

• If you are going to use SCSI as the bootable hard drive in a computer, you will have to check the documentation that comes with the host cards. Often they will require that the bootable drive be set to a particular ID number.

There are various methods for setting SCSI IDs. They will usually take the form of jumpers or switches. Some SCSI devices provide a set of four switches. Each switch represents one digit of a binary number. To set the ID number 0, all would be off. The ID number 7 would be all on. Any number in between will be based on the correct binary digits being on or off.

SCSI ID 7 has the highest priority followed by 6, 5, 4, 3, 2, 1 and 0, then by 15, 14, 13, 12, 11, 10, 9 and 8.

WARNING: Some external devices will have a limited number of choices. This lack of choices may cause some problems when the chain is full. You may have to adjust other drive IDs in order to find a unique ID for the new one.

Rule # 3 – Set the Logical Unit Numbers (LUN)

SCSI hard drives have gained a great deal of popularity in networking and environments that require the storage of large amounts of data. Because SCSI can transfer files between devices on the chain without interrupting the processor, they are often configured into an array of disks. This array allows for storage of very large amounts of data and creation of automatic backups. It is possible to have a single SCSI ID support more than one device, thus increasing the size of the storage array. The use of Logical Unit Numbers with a SCSI ID number will provide up to seven additional sub-IDs per ID number.

SCSI Standards

SCSI is a standard that defines the hardware parameters (physical and electrical) of a parallel I/O bus that is used to connect several devices in a daisy chain fashion. The original SCSI standard is based on ANSI X3.131-1986 and has grown to three levels with some variations of each. One of the problems with using SCSI is that not all SCSI is the same. As a technician, you will need to be familiar with the different types so that if you are expanding a SCSI system, you will be able to specify the correct devices. In addition, you will find many devices today that claim to be SCSI, but connect to a parallel port. While these are true SCSI devices, they are a stripped-down version and will not have all the advantages of a true SCSI chain. Lets now look at the basic SCSI standards and how they differ.

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Single-ended SCSI (SE) vs. High Voltage Differential SCSI (HVD)

The original or normal SCSI is called single-ended SCSI or SE for short. With this type of SCSI, there is one wire for each signal on the bus. This may not seem astonishing, but this format imposes a 6-meter (19.7 feet) limit on cable length. This is reduced to 3-meters (9.8 feet) when using what is known as fast SCSI. For most computer systems, this is not problem, but to overcome this and allow for up to 25-meters (82 feet) of cable, SCSI employs High Voltage Differential SCSI or HVD. HVD SCSI uses two wires for each signal on the bus. The second wire carries the logical inversion of the signal on the first wire. HVD SCSI is used on high-end applications because it not only allows for longer cabling, but it is better at rejecting noise. It is important that you can tell the difference between SE and HVD SCSI systems. The reason behind this is that you cannot connect SE and HVD devices on the same SCSI chain. The result will be damage to one or more devices. It will be very easy to tell which device is damaged – just look for the smoke. The following are the official symbols for both single-ended and high voltage differential SCSI.

Single-ended and High Voltage Differential SCSI

Low-Voltage Differential SCSI (LVD)

HVD uses two wires to improve signal integrity, but is expensive to implement and uses a lot of power. Because of this, it has never become popular and the SE signaling system has been the standard. However, once the SCSI standards were ready to implement the 40 MHz bus, it quickly became apparent that SE would not suffice. The 20 MHz bus had already reduced the cable length to 1.5 meters, and with the 40 MHZ bus this length is reduced to only .75 meters. As that is just a little over 2 feet for the entire chain, it was quickly understood that there was a serious problem and a new signaling method would be needed in order to increase the bus speed of SCSI.

Enter Low-Voltage Differential (LVD). This technology married the best of the SE and HVD signaling methods to create a signaling method that is designed to use the advantages of differential signaling (two wires) to allow for long cable lengths. At the same time, it would reduce implementation and power costs, and would be compatible with SE devices.

This signaling method has become so popular that it is expected to become the industry standard in a very short time. Its success is mostly due to its ability to offer a cost-effective means to deliver faster SCSI bus speeds over longer cables. SE devices are electrically compatible with LVD and some LVD devices are even compatible with SE. These devices are known as multimode LVD devices and are abbreviated (LVD/SE) or LVD/MSE. These devices will automatically switch between LVD and SE operation by

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detecting what other devices on the chain are running in. It should be noted however, that only one or the other may be used at a time (SE or LVD).

LVD still adheres to the standard SCSI rules regarding unique IDs and termination, but in addition, LVD operation requires the following:

• All devices on a chain must be LVD-capable. If even one device is SE, the entire chain will have to run as SE.

• If even one device in a chain is jumpered to run in SE mode, this will cause the entire chain not to run in LVD.

• LVD terminators must be used.

Keep in mind that once the chain begins to operate under SE, all the rules associated with SE will apply to the entire chain. (Such as signal speeds and cable lengths.)

The following symbols are used to identify LVD devices:

SCSI LVD and SCSI LVD/SE

SCSI-1 and SCSI-2

SCSI-1 and SCSI-2 are essentially the same standard. SCSI-2 is an upgrade and completely compatible with SCSI-1. While SCSI-2 has a few more features, these are just ignored by any SCSI-1 device if used on the same bus. The SCSI-1 & -2 standards include the following:

• SCSI-1 – This will allow data transfer speeds of 5 MB/sec, uses the narrow bus (8-bit), uses the single end or differential signaling method, and can support up to 8 devices. It must be terminated using passive, active or forced perfect termination and uses the “A” type cable (50-pins) and has a maximum cable length of 6 meters for single-ended and 25 meters for differential.

• SCSI-2 – This has the same specs as SCSI-1 except that it supports an increased data transfer speed of 10 MB/sec. SCSI-2 also supports command queuing which allows an operating system to send multiple commands to the SCSI host adapter without having to order them.

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• Fast SCSI – This will allow increased data transfer speeds of 10 MB/sec on standard 8-bit cabling and 20 MB/sec when combined with 16-bit wide SCSI.

• Fast Wide SCSI – As the name implies this uses the wide (16-bit) bus and supports data transfer speeds of 20 MB/sec. It can support up to 16 devices using the type “P” (68-pins) cable.

• Wide SCSI – This increases the bus width from 8-bit to 16-bit allowing for faster data transfers.

• Command Queuing – SCSI-1 could only send one command to a device at a time. With command queuing, 256 commands can be sent at one time and placed into a queue for execution.

• Active Termination – SCSI-2 can use a voltage-regulated terminator that lowers the impedance to 110 ohms and improves system integrity.

• There was actually a 32-bit (extra-wide) SCSI standard developed under the SCSI-2 standards. It was unsuccessful and has been withdrawn from the standards.

SCSI-3

SCSI-3 consists of a set of primary commands and additional command sets that meet the needs of specific device types. It contains a collection of command sets for not only the SCSI-3 parallel interface, but also for additional parallel and serial protocols, including Fiber Channel, IEEE 1394 (Firewire), and the Serial Storage Protocol (SSP).

Development of the SCSI 3 standards began in 1993. Because the standard included so much more technology than the SCSI-1 and SCSI-2 standards, it would have been impossible to include the standards in one large document as was done with SCSI-1 & 2. Recognizing this, it was decided to make SCSI-3 a collection of different but related standards. Each of these standards has a name and is revised independently. This makes for a lot of confusion and it is unclear as to whether the overall “SCSI-3” standard will ever be formally approved. So many SCSI and “SCSI-like” devices are included under this umbrella of standards, that it is possible to find devices that are labeled SCSI-3 that don’t even use the same physical interface or commands.

The industry is considering separating out the different standards and renaming them. Unfortunately, this would probably cause even more confusion.

Fiber Channel SCSI

This is a specification for fiber optic and coaxial cable SCSI devices. It can achieve 100 MB/sec data transfer rates.

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Some of the specifications of the SCSI-3 standards include:

• Ultra SCSI (including Fast –20 SCSI Addendum) – This uses the wide (16-bit) bus with data transfer speeds of up to 20 MB/sec. It will support up to 4 devices if the single-ended signaling method is used, and up to 8 using the differential-ended signaling method. It uses the type “A” cable (50-pin) with a maximum length of 3 meters if no more than 4 devices are used, otherwise 1.5 meters is the maximum cable length.

• Wide Ultra SCSI (including Fast-20 SCSI Addendum) - This uses the wide (16-bit) bus with data transfer speeds of up to 40 MB/sec. It will support up to 8 devices if the single-ended signaling method is used, or up to 4 if the cable length is over 1.5 meters. It will support up to 16 devices using the differential-ended signaling method. It uses the type “P” cable (68-pin) with a maximum length of 3 meters if no more than 4 devices are used, otherwise 1.5 meters is the maximum cable length when using the single –ended signaling method. If the differential-ended signaling method is used, cable lengths can be up to 25 meters.

• Ultra2 SCSI (sometimes called Fast-40 SCSI) – This SCSI-3 standard was originally defined using the narrow (8-bit) bus, however, this never caught on. It uses the “A” type cable (50-pins) and either the LVD or HVD signaling method (the HVD method is not often used). It can support up to 8 devices using HVD or LVD with cables up to 12 meters in lengths. It can support 2 LVD devices when cable lengths exceed 12 meters.

• Wide Ultra2 SCSI – This uses the wide (16-bit) bus to gain throughput of 80 MB/sec. It uses the LVD signaling method, but can (but rarely does) use the HVD method. It uses the “P” type cable (68-pins), and it can support up to 16 devices using HVD or LVD cables up to 12 meters, or 2 LVD devices on cables over 12 meters.

• Ultra3 SCSI - This standard uses the wide (16-bit) bus type and the narrow bus is not supported at all. It has transfer speeds of up to 160 MB/sec and uses the LVD signaling method only. It supports up to 16 devices for type “P” (68-pin) cables of up to 12 meters or up to 2 devices for longer cables.

• Ultra160 SCSI – Many hardware developers felt that there would be compatibility issues with this technology if they used the SCSI-3 standard to identify these products. To avoid possible confusion several companies decided to create a specific feature set that is called Ultra160/m. The “m” means “maximum” or possible “manageability” depending on whom you ask. The “m” was later dropped and it is now simply referred to as Ultra160. (So much for avoiding confusion! Just be aware that Ultra160 and Ultra160/m are the same.) This uses the wide (16-bit) bus and once again, the narrow bus is not supported. It uses the LVD signaling method, but if using multimode devices can optionally run in SE mode. Running is SE mode will, however, limit transfer speeds to 20 MB/sec. It uses the “P” cable type (68-pin) and will support up to 16 devices for cables up to 12 meters and up to 2 devices for longer cable lengths.

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• Ultra160+ SCSI – This is simply a version of the Ultra160 SCSI that contains some additional features. Its specifications are mostly the same.

• Ultra320 SCSI –This is the next generation of SCSI that is currently in development. As the name implies, it will support data transfer speeds of 320 MB/sec. It originally was called Ultra4 SCSI, but it appears that this name has not been adopted by the industry, so it is called Ultra320. It will use the LVD signaling method, but will optionally support SE devices, with the resulting drop in speeds. It will use the “P” cable type (68-pin) and can support up to 16 devices on cables up to 12 meters in length or 2 devices for cables over 12 meters.

As you have noticed by now, there are many different “flavors” of SCSI. It is not important that you memorize all the different types, but you will need a basic understanding of the technologies. Fortunately, in the real world, SCSI hardware is well engineered and is designed to allow different hardware types to work together easily.

The following table compares the more popular SCSI standards:

SCSI standards

SCSI Type Maximum Number of Devices

Maximum Speed (MBps)

Maximum Cable Length (meter)

SCSI-1 8 5 6

SCSI-2 8 or 16 5-10 6

Fast 8 10-20 3

SCSI-2 16 20 3

Wide SCSI-2 16 20 3

Ultra SCSI 8 20 1.5

Ultra SCSI 16 40 1.5

Ultra 8 40 12

Wide Ultra 16 80 12

Ultra 16 160 12

Note: SCSI-2 and SCSI-3 presently lead the pack in popularity.

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SCSI cabling

There is no single standard for SCSI cabling. The only way to be sure is to check the documentation for the device you are going to use. Internal SCSI devices are connected to the host adapter through the internal connector and a 50-pin ribbon cable (similar to a 40-pin IDE cable). These cables are used for 8-bit data transfer devices. On SCSI devices that achieve 16-bit data transfers, use two cables. The 50-pin cable is combined with a 68-pin cable. External connectors are typically twisted multiwire-shielded cables with a plastic coating. Again, the connectors will vary from manufacturer to manufacturer. For example, Macintosh uses different cables than non-Macintosh manufacturers.

WARNING: Unlike IDE devices, if SCSI devices are plugged incorrectly (i.e. cable in backwards), they can be damaged!

SCSI cabling can be summarized into the following types:

• SCSI Type “A” Cable – 8-bit Narrow SCSI – 50-pin

• SCSI Type “B” Cable – 16-bit SCSI 2 devices – 68 pin

• SCSI Type “P” Cable – 16-bit SCSI 3 wide devices – 68 pin

• SCSI Type “Q” Cable –SCSI 3 devices – 68-pin

The only way to be sure of which cable combination to use is to read the documentation and look at the devices and connectors.

SCSI Drivers

All SCSI peripheral devices attached to a host must have some sort of software or driver installed in order for it to work. They are no different from any other peripheral device that you install. The only exceptions to this are SCSI hard drives. The drivers for these devices are usually provided as part of the host adapter BIOS. To simplify the creation of drivers for peripheral devices, two common interfaces have been developed. As long as the drive is written to “talk” through one of these common interfaces, the device will work. The most popular interface used today is ASPI (Advanced SCSI Programming Interface). Windows 9x, Windows NT, OS/2, 2.1 and later, provide automatic support for this interface. The second interface in common use is CAM (Common Access Method). You can also find some CAM-to-ASPI converter utilities to provide cross-platform support.

Advantages of SCSI

At the beginning of this section, we pointed out that the main disadvantage of SCSI was cost. In most circumstances, implementation of a SCSI system will certainly cost more. In addition, if you were to compare identical SCSI and IDE drives on a task-per-task basis, you will find that the IDE actually outperforms SCSI. Knowing this, you may ask, why bother with SCSI? The answer is simple, when you implement SCSI; you are not

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implementing a drive, but a bus. It is taking advantage of the features of the bus that make SCSI worthwhile. Lets look at how we can take advantage of SCSI by starting with bus mastering.

Bus Mastering is a term that you may encounter in several contexts. In this example, we are talking about comparing transferring data on non-SCSI systems verses SCSI systems. In a non-SCSI system, the CPU must manage all the activity. SCSI on the other hand, allows devices to perform these functions independently of the CPU by providing a way for devices to disconnect from the motherboard bus and use the SCSI bus. In this case, the host adapter will take charge or master the bus. For example, you need to backup one of the hard drives on a SCSI bus to a tape drive on the same bus. Once the backup is initiated, the host adapter will disconnect from the motherboard bus and transfer the data between the hard drive and the tape drive without bothering the CPU.

Earlier, we mentioned that SCSI is often the choice for networks and systems that store large amounts of data. In particular, we are looking at large network servers that are responsible for storing and safeguarding large amounts of data. The solution to these problems is to use a large array of disks often called RAID. RAID means Redundant Array of Inexpensive Disks.

Because a SCSI bus uses bus mastering, writing redundant data over several drives does not impose additional overhead on the CPU. Using RAID can allow for fault-tolerance. That means providing automatic backup in the event of problems. RAID is provided in several different levels, each increasing in complexity but providing higher levels of security. Let’s look at the different levels of RAID:

RAID 0

RAID level 0 uses data striping and block interleaving. This process involves distributing the data block-by-block across a disk array. Data can be read or written to the same sector from either disk, thus improving performance. RAID 0 requires at least two disks and the striped partitions must be the same size. RAID 0 does not provide fault-tolerance as failure of one drive can bring down the entire system.

RAID 1

RAID level 1 is known disk mirroring or disk duplexing. With disk mirroring, data is written to two disk drives at the same time using a single channel. If one drive fails, the data is still available on the other drive.

RAID 2

RAID 2 uses data striping. This writes data over an array of as many as a dozen hard disks. Data is duplicated on several different disks that will enable error corrections.

RAID 3

Level 3 is the same as level 2, but it provides an additional parity bit for error corrections. This increases the reliability of RAID 3 over RAID 2.

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RAID 4

RAID 4 is like 3, but it writes data one sector at a time.

RAID 5

This is the most popular form of RAID. It is an improvement of RAID 4. The difference is that the parity information is distributed across the regular disk, rather than being written to a special disk. RAID 5 is also known as disk striping with parity and has a level of fault tolerance.

RAID 6

RAID 6 will allow for up to two disks to fail without loss of data. It is similar to 5, but it distributes two copies of the error-checking data across the array.

USB Drives

These drives employ flash memory for portable storage. They can generally hold up to 128 MB worth of data, but some hold as much as 1 GB (these are quite cost prohibitive). These drives are plugged into a USB port and don’t require drivers. They also contain their own CPU.

USB drives are known by a variety of names such as:

• Pen drive

• Keychain drive

• Memory Key

• Thumb drive

USB Drive

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Optical Drives

The latest technology to come of age for storing data belongs to the family of optical drives. Most of us are familiar with the CD-ROMs that we use for playing audio or installing software. The big advantage of these drives is that they can store large amounts of data and are inexpensive to produce. CD-ROMs are only one part of this family of drives used with computers. This section will explore the CD-ROM as an essential part of today’s computers and look at what is in store for the future.

CD-ROMs

The CD-ROM (Compact Disk - Read Only Memory) is a technology taken directly from the audio world and has become “standard equipment” for new computers. If a hard drive holds more information, accesses the information faster, and reads and writes information, then why do we need CD-ROMs? The answer is simple; a CD can hold large amounts of data (650 Meg) and can be mass-produced at a very low cost.

The CD has become the media of choice for software manufacturers. An entire software package can be stored on one CD. For example, early versions of the Microsoft Office Suite were supplied on 32 disks. Today, the entire program and manuals, are stored on one CD. Installation time from a CD is also much reduced and easier (turn it on and come back later as opposed to sitting and feeding your computer disk after disk).

Early CDs were used to store such information as large databases (entire encyclopedias) and play music. Now they can contain video clips, sound clips and animation. Entire phone listings for the US are also available on CD. The following table summarizes the advantages of CD-ROMs.

Advantages of CD-ROM

High Storage Capacity

Up to 650 Megs of data on 4 ½ -inch disk. (Smaller than the original 5 ¼ and holds almost 2000 times as much information).

Portability Portable and replaceable medium.

Data Cannot Be Changed

Read-Only (WORM, Write Once Read Many Drives are on the market and developing fast.) This will prevent accidental erasure of programs or files.

Sturdiness More durable than the standard 5¼ or 3½ disks.

Special Capabilities Audio capable, special compression of audio, image and video data.

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Note: CD-ROMs have an eject hole which can be used to pop the drive open in the event that the CD-ROM drive won’t open on its own. Just use a straightened-out paperclip to pop the drive open.

CD Technology

The CD, as a storage media, began to show up in the audio industry in 1979. In 1985, the CD came to the computer industry and development was slow because the hardware was too expensive. In 1991, the CD-ROM/XA standard was enhanced and multimedia requirements for hardware specified. 1993 brought quality video playback to the computer.

Today, prices continue to drop and the speed of drives continues to climb. It is rare if a computer manufactured today does not have a CD-ROM drive installed as standard equipment. Most software packages are shipped in CD-ROM versions (3½-inch diskette versions are available but require special ordering and often do not contain all the extras that the CD version does).

Storing Data

Data on a CD-ROM is stored as a series of ones and zeros just like a diskette. However, instead of using a magnetic surface for storing the data, the CD uses laser technology. There are two major advantages for using lasers: First, there is no physical contact between the surface of the CD and the reading device; Second, the diameter of the laser beam is so small, storage tracks can be very close together, thereby storing more data in a smaller place.

A CD is made of a reflective layer of aluminum applied to a synthetic base, with a layer of transparent polycarbonate as a cover. A protective coating of lacquer is applied to the surface to protect it from dust, dirt and scratches. The data is stored by creating “pits” and “lands” on the surface. A pit is a depression on the surface and a land is the original surface. The transition from a land to a pit or a pit to a land represents binary 1. Lands and pits represent binary 0. There are approximately 4-5 million pits per CD. They are arranged in a single outward running spiral (track) approximately 3.75 miles (6 kilometers) long. The distance between each element is 1.6 thousandths of a millimeter.

Connections

A CD-ROM is a peripheral device and must be connected to the bus of the computer through a controller. There are several options for installing a CD-ROM.

Some CD-ROM manufacturers provide a proprietary adapter board made specifically for their product. These boards are supplied with the drive and are not usually interchangeable. Many sound cards have built-in CD-ROM controllers. Most sound cards come with a 15-pin female connector known as the MIDI (Musical Instrument Digital Interface) connector. Some of the newer cards come with a SCSI interface.

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The use of a SCSI interface is very popular with CD-ROMs. These interfaces operate at higher processing speeds than other interfaces. Many of the high-speed drives use this interface to take advantage of the speed. A SCSI CD-ROM can be installed in any SCSI chain. In situations where very large amounts of data must be stored and remain accessible to users, it is common to have several CD-ROM drives connected to one SCSI controller. Just think, if one CD can hold 650 MB of data, six can contain almost 4 GB of data! This may not seem like much with today’s large hard drives, but remember, you can change them as you wish. SCSI adapters can be purchased that connect directly to a parallel port on the computer. However, data transfer is somewhat slower than if connected directly to a SCSI controller card.

Note: Today, the trend is moving back to the hard drive as the primary storage media. With the cost of these drives falling and the amount of data storage available rising, the hard drive is still king of the storage media. Optical data storage (CD) holds its place as removable media and as the media of choice for archival data storage. It is also the choice for software manufacturers for installing software.

Audio Capability

Any CD-ROM drive that meets the Yellow Book standards (a standard created by the audio industry for sound and has been adopted by the computer industry), has the ability to play back audio CDs. Most CD-ROM drives contain the circuitry and chips to convert digital audio data back to sound data. Most drives (and sound cards) have a headphone jack and audio jacks to connect to a stereo system. The only requirement is that the drive supports the ISO 9660 (International Standards Organization) standard for the file systems. ISO 9660 is also known as the High Sierra Format.

Speed and Access Time

When purchasing or specifying a CD-ROM, two values need to be considered. The first is the data transfer rate. The long-time standard for transfer rate has been 150K/s (Kilobytes per second). This value is the basis for measuring CDs today. A 2x CD operates at 300K/s, a 4x at 600K/s and so on. A typical CD-ROM today will operate at 48x or even as high as 72x.

The second value to look at is mean access time. This is the time it takes the head to move over half of the tracks. Typical access time is 200 to 400 ms (micro seconds). Note, although the transfer rate increases in multiples, the mean access time does not. The following table lists transfer rates and access speeds for some common CD-ROMs.

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CD-ROM – Transfer Rate and Access Time

CD-ROM Speed Transfer Rate Access Speed

4x 600Kps 1500ms

6x 900Kps 150ms

8x 1200Kps 100ms

12x 1800Kps 100ms

16x 2.4Mbps 90ms

24x 3.6Mbps 90ms

32x 4.8Mbps 85ms

100x 15Mbps 80ms

Recordable CD (CD-R)

The RO in CD-ROM stands for Read Only. For years, CDs have been read-only, but recently this has changed (for the better). This wonderful media is responsible for revolutionizing the way that we obtain data, but unfortunately, hardly anyone has their own CD press, and if you wanted to re-produce your own CDs, the cost was prohibitive unless you were going to have thousands made. With CD-R, it is now possible to record on CD from the comfort of your desktop.

Philips published the standards for CD-R or Recordable CD in something called the “Orange Book” in 1990. This technology is sometimes called CD-WORM (Compact Disk-Write Once Read Many), but this is confusing because there are other types of technology that share this name.

When CD-R first appeared, it was prohibitively expensive at over $1,000 per drive, and about $10.00 or more for each disk. Fortunately, these costs have decreased dramatically, and are now within reach of most consumers.

CD-R Encoding

In order for CD-R to write a CD without the previous costly technology, the pits and lands have been done away with. The CD-R disks use the same polycarbonate substrate as the CD-ROM, but instead of physically etching the surface, it is stamped with a spiral pre-groove. This pre-groove is similar to the spiral found on a regular CD, except that it is intentionally “wobbled.” The CD-R drive uses this groove to follow the data path during recording. This pre-grooving simplifies the complex process of creating these tracks during recording, because the tracks are only 1.6 microns apart.

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CD-R disks do not look the same as a regular CD. This is because a photosensitive dye layer is placed on top of the polycarbonate layer and a metal reflective layer (such as a gold or silver alloy) is placed on top of that. A special laser that is used in the drive causes the dye layer to react a certain way when applied. Many technicians refer to creating a CD as “burning.” This is mostly correct. The effect of the laser on the “burned” areas of the disk causes the disk to reflect less light than the “non-burned” areas, thereby emulating the “pits” and “lands” of a regular CD.

CD-R Compatibility with CD-ROM

Usually disks created with CD-R are compatible with most CD-ROM and CD audio players. There can be problems, however, especially with older CD-ROM drives. This can sometimes be handled by changing to a different brand of CD-R. CD-R blanks are inexpensive, but sometimes the less expensive ones may not perform as expected.

CD-R Software

Special software is required to run CD-R drives and most drives come with the software. The quality of this software has a direct impact on how easy (or how difficult) it is to create CDs. Before purchasing a CD-R drive, find out what kind of software comes with it and make sure that it will suit your needs.

CD-R Drives

As we previously mentioned, CD-R drives use a special laser. This laser is different because it must burn the image onto the media as well as read the media. These drives typically can read a variety of CD types and are not limited to CDs created by them. CD-R drives usually have a different speed for reading and writing. As you might suspect, the write speed will be slower.

When burning a CD-R, the drive requires a constant flow of data and any interruption will usually cause the CD-R to be ruined. You should always test a freshly burned CD to make sure that the data was transferred as you expected.

ReWritable CD (CD-RW)

The next obvious step in CD technology was the rewritable CD. Just like the classic floppy disk, these can be erased and reused. In fact, sometimes this technology will be referred to as Erasable CD or CD-E. Although this sounds like the perfect CD technology, you should be aware that certain compatibility issues with other CD types could arise with this media.

CD-RW Encoding

The media for CD-RW is very similar to CD-R. The difference is that the dye layer is a special phase-changing recording layer. It is comprised of a chemical compound that changes state when light is applied, and it can change back again. This phase-changing layer is not permanently “burned” as is the CD-R dye layer and can be returned to its original state.

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The important drawback to this is that they don’t emulate the pits and lands well enough for all regular CD and CD-R drives to read, and therefore are not backward compatible with all CD players. This is because the surface has a lower reflectivity and regular drives may have trouble reading them.

Please note: the media itself causes the problem, not the drive. For example, a CD-R disk that is made in a CD-RW drive can be read from any CD player that is capable of reading CD-R media. The compatibility issues are with the media (disks) not with the drive.

Installing a CD-ROM

Installing a CD-ROM drive is very similar to installing a hard drive. Newer computers have primary and secondary IDE connectors as part of the motherboard and BIOS setup. It is becoming commonplace to install CD-ROMs on the secondary port. Installing a CD-ROM is a three-step process.

• Install the drive controller card.

• Install the CD-ROM into the case.

• Install the necessary drivers and set-up.

Controller Cards

The most difficult part of a CD-ROM installation is determining which controller card is best for the system. There are several possible combinations for controller cards.

• Use the secondary IDE controller on the motherboard.

• Install a new controller card (supplied with the CD-ROM).

• Install in an existing SCSI chain.

• Install a SCSI host adapter and create a new SCSI chain.

• Confirm that the IRQ setting is correct.

• Use an existing sound card with a CD connection.

A quick review of the computer resources (both used and available) will guide you in the selection of the proper card. In some cases, any available set-up will work, in other cases; there may be only one choice. Whichever card arrangement is chosen, be sure to disable any other possible conflicting cards. Confirm the computers’ resources before purchasing a new CD-ROM. This may save the time and frustration of having to return or exchange it.

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Installing in the Computer

A CD-ROM will mount easily into any computer that has an open bay for a 5¼-inch disk drive. Physical installation is as simple as installing a floppy disk drive. Most new CD-ROMs come with a hardware kit, which includes a combination of screws and brackets.

Make sure you have all the tools and parts before beginning.

• The CD-ROM drive

• The correct cables

• The appropriate hardware

• The appropriate tools Flathead screwdriver Phillips-head screwdriver Needle-nose pliers or tweezers (for jumper settings)

Cable connections are as simple as installing a floppy disk drive. There will be two cables - a flat ribbon cable (for data) and a power cable. Be sure to connect wire number 1 to the correct location on both the controller and the CD. If there are no available power cables, use a Y power splitter cable. There may also be an audio-out cable (two to four wires) connected to the sound card. This connection will allow you to take full advantage of the audio capabilities of the CD-ROM.

Cable Connections to back of Typical CD-ROM

Software Set-Up

While the use of software such as DOS and Windows is covered in more detail later in this course, it is important to include the basics here. You may need to come back later and review this after completing the course. The file directory for a CD-ROM is different from the directory used by DOS’s file allocation table (FAT). Therefore, a special driver is necessary for DOS to be able to recognize this device as a drive. A standard device driver supplied by the manufacturer (for BIOS) will also be required.

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Windows 3.x

Microsoft’s MSCDEX.EXE, a DOS resident application, provides the required translation. MSCDEX.EXE also specifies the device driver required by the device. The following changes in CONFIG.SYS and AUTOEXEC.BAT (or something similar) will do the job.

CONFIG.SYS

To load the device driver

device =C:\CDROM\MTMCDAI.SYS /D:MSCD001 (include directory and driver for the CD to be installed)

To insure drive number assignment space

lastdrive = z

AUTOEXEC.BAT

C:\DOS\MSCDEX.EXE /D:MSCD001 /L:E /M:10

Most CD-ROM installation diskettes will make these changes automatically. Additional information for configuring CONFIG.SYS and AUTOEXEC.BAT is found in the Software sections of this text.

Windows 9x

Windows 9x uses a 32-bit protected-mode driver named VCDFSD.VXD. This driver replaced MSCDEX.EXE, the real mode driver. When adding a new CD after Windows 9x has been installed, be sure to use the Add New Hardware Wizard. This wizard will properly identify and set-up the CD.

NOTE: If you intend to use a CD-ROM in the DOS mode (from a bootable disk), the real mode drivers will have to be installed and added to the CONFIG.SYS and AUTOEXEC.BAT files of the boot disk.

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Maintaining a CD-ROM

CD-ROM drives have a reputation for being trouble free. This doesn’t mean that they never fail, just that you should not expect to have any problems. Troubleshooting a CD-ROM drive is the same as troubleshooting a floppy drive.

• Check the cables.

• BIOS/CMOS – most CDs are configured through installation of software drivers. Make sure that the files have not been corrupted and that any statements in the CONFIG.SYS or AUTOEXEC.BAT files are correct.

• Check the drive – there are few things that can go wrong with the drive, however the opening and closing of the access drawer can cause problems induced by jams.

• The controller – CDs use controllers just like other drives.

Multimedia

A sound card is essential if you want to turn your computer into a multimedia computer. What is multimedia? The term embraces a number of computer technologies, but multimedia primarily deals with video, sound and storage. Multimedia is a combination of graphics, data and sound on a computer. In all practicality, multimedia simply means adding and configuring a sound card and a CD-ROM drive to a system.

Microsoft originally formed an organization called the Multimedia Marketing Council (MMC) in 1991 to generate standards for multimedia computers. They created several standards and they license their logo and trademark to manufacturers whose hardware and software conform to these standards. The standards enable companies to develop compatible hardware and software for multimedia operations on computer-compatible systems.

Recently, the Multimedia PC Marketing Council formally transferred responsibility for their standards to the Software Publishers Association’s Multimedia PC Working Group. This group includes many of the same members as the original MMC and is now the body governing the MMC specifications. The group’s first creation was a new Multimedia PC (MPC) standard.

The MPC Marketing Council originally developed two primary standards for multimedia: MPC Level 1 and MPC Level 2. Under the direction of the Software Publishers Association (SPA), the first two standards have been replaced by a third standard called MPC Level 3, which SPA introduced in June 1995. These standards define the minimum capabilities for a multimedia computer.

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The following table shows these standards:

MULTIMEDIA STANDARDS

MPC LEVEL 1 MPC LEVEL 2 MPC LEVEL 3

Processor 16 MHz 386SX 25 MHz 486SX 75+ MHz

RAM 2 MB 4 MB 8 MB

Hard Disk 30 MB 160 MB 540 MB

Floppy Disk 1.44 MB 3.5” 1.44 MB 3.5” 1.44 MB 3.5”

CD-ROM Single-Speed Double-Speed Quad-Speed

Audio 8-bit 16-bit 16-bit

VGA Video Resolution

640x480; 16 colors

640x480; 64K colors

640x480; 64K colors

Other I/O Serial; Parallel; MIDI; Game

Serial; Parallel; MIDI; Game

Serial; Parallel; MIDI; Game

Software Microsoft Windows 3.1

Microsoft Windows 3.1

Microsoft Windows 3.1

Date Introduced

1993 1994 1995

You should consider the MPC-3 specifications the bare minimums for any multimedia system today. Specifically, a recommended system exceeds the Level 3 standards in several areas, such as RAM, hard disk size and video capability. Although speakers are not technically a part of the MPC specification, all sound reproduction does require speakers!

Video Capture Software

With the advent of multimedia computers and software, manipulating full motion video was the next logical step in computer technology. A modern high-speed multimedia computer has become standard equipment in the moviemaking industry. Now even amateur moviemakers can use their computers to give their home movies a touch of professionalism.

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Video capture software provides an interface to capture and configure video into (and out of) a computer. This software allows the user to view audio waveforms and video images, create files, capture single frame or full-motion video and edit video clips and still-frames for content and effects.

File editing functions such as, zoom, undo, cut, paste, crop and clear can be used to edit both audio and visual files. Users can also set the compression controls to the type of format desired and set the capture rates. The standard capture rate for full-motion video is 30 frames per second (fps), but some systems may not be able to reach this potential. Professional systems include very large, very fast hard drives for data buffering. A typical user of video capture software may only realize a frame capture rate of up to 15 fps without adding an arsenal of hardware to enhance the system.

Other Optical Drives

We have discussed the use of a CD-ROM for computers. You may encounter several other optical devices as well. The term optical drive is a generic term for several devices. Optical technology involves the storing of data on a rigid disk by altering the disk’s physical characteristics with a laser beam. Once the disk is altered, the differences in reflectivity or polarization can be “read” as a binary “1” or “0.” The use of laser color, power or a combination of both determines whether it is a read or write operation. Any device that uses this technology, including CD, is considered optical. The following is a description of some of the new optical technology.

WORM (Write Once-Read Many)

WORM uses laser technology to permanently alter sectors of the disk thereby permanently writing files onto the media. With a WORM drive, a computer operator can create CDs. Since this alteration is permanent, the device can only write once to each disk. WORM optical disks come in a protective case similar to, but stronger than, the case for a 3½ -inch diskette. While most of us think in terms of the 5¼-inch drives common to CDs, WORM can also come in 4-inch and 12-inch disks.

The 5¼-inch WORM has various ISO standards in place to minimize potential forced data migration and associated switching costs. ISO 13346, the Universal Disk Format, allows 5¼-inch optical disks to be interchangeable between vendors supporting the standard. UDF writes the file system onto the disk and provides interchangeability similar to a DOS diskette or Zip disk.

Digital Versatile/Video Disk (DVD)

The DVD family of formats will replace the CD-ROM family of formats over the next couple of years. DVD sometimes stands for Digital Versatile Disk, and sometimes Digital Video Disk, depending on who is asked. DVD is newer and hence relatively immature, but it promises more space that CD and therefore is very desirable. DVD has five formats: DVD-ROM, DVD-Video, DVD-Audio, DVD-R and DVD-RAM. DVD-R is the format for write-once. It specifies 3.95GB for single-sided and 7.9GB for double-sided. DVD-RAM is the format for rewritable. It specifies 2.6GB for single-sided and

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5.2GB for double-sided, with a disk cartridge as an option. DVD-ROM (read-only disks) are similar to CD-ROMs and have a 4.7GB (single-sided, single-layer), 9.4GB (double-sided, single-layer), 8.5GB (double-layer, single-sided), 17GB (dual-layer, double-sided). These are backward compatible with CD-audio and CD-ROM. DVD-ROM drives can play DVD-R, in fact, all of the DVD formats. UDF is the file system for DVD-R. Don’t be surprised if DVD replaces the VCR in the future.

Rewritable Optical

Two new technologies are being employed which use rewritable optical technology. These technologies are called MO (Magneto-Optical) and PCR (Phase Change Rewritable). MO drives are more widely accepted because the media and drive manufacturers use the same standards and are cross compatible. PCR devices on the other hand, come from one manufacturer (Matsushita/Panasonic) and the media comes from two manufacturers (Panasonic and Plasmon).

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Summary

This has been a long and information-packed chapter. The concepts covered in this chapter are extremely important to the A+ Technician, both for the test and for the real world. We strongly recommend that you study these concepts until you have a firm grasp on the material.

Floppy Disks

• The first disk drives were floppy drives. The technology of floppies has changed little in the past few years.

• The 3½-inch floppy has become a standard of computers.

• Floppy drives are designated as A or B. The drive letter designation is determined by the location of the drive on the cable.

• Floppy drives use a 34-pin ribbon cable with a twist to differentiate between the A and the B drive.

Hard Drives

• The maximum storage capacity of a hard drive is determined by its geometry.

• CHS values define the geometry of a hard drive.

• Proper CMOS settings are required for hard drives.

• There are two types of partitions – primary and extended.

• A cluster is the basic unit of storage.

• The three major steps after installing a hard drive are to partition the drive, set up the CMOS settings and format the drive.

• FDISK is used to partition hard drives. A computer technician should be familiar with the use of FDISK and partitioning.

• The geometry of a hard drive (CHS values) determines its storage capacity.

• There are two types of partitions (primary and extended). DOS must be on the primary partition.

• An active partition stores the operating system. The active partition is usually (but not always) the primary partition.

• Early BIOS limited hard drive sizes to 504MB (528 megabytes).

• Using new technology, the hard drive limit has been exceeded.

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• Modern computers allow up to 4 IDE drives to be installed on built-in controllers.

• Properly setting Programmed I/O will enhance the performance of a drive.

• EIDE brought four major upgrades; LBA translation, Programmed I/O Modes 3 & 4, allows CD-ROM and Tape backup from same controller and supports secondary controller (allows 4 drives).

• Traditional SCSI chains allow for up to 8 devices (including the host controller) to be connected together. Some of the newer SCSI standards allow for up to 16 devices to be chained.

• SCSI chains must be terminated at both ends.

• Each device on a SCSI chain must have a unique ID.

• RAID uses SCSI drives to provide improved data storage and fault tolerance.

Optical Drives

• A CD-ROM is now a standard part of a computer system.

• CD-ROM transfer rates are based on a factor of 150 KBps.

• CD-R and CD-RW are popular emerging technologies. Understand the concepts behind these new drives and compatibility issues.

• Installing a CD is as easy as installing a floppy drive.

• The proper drivers must be loaded before the processor can access a CD-ROM.

• To run a CD-ROM from DOS, the real-mode drivers must be loaded.

• A CD-ROM is an essential part of the multimedia standard.

• DVD is the latest technology that offers dramatically increased storage space. It has the potential to replace VHS and even possibly CD-ROM technology.

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KEYWORDS Exercise

Define each of the following keywords. Hint: There’s a glossary in the back of this book.

Keyword Definition

Active Termination

ATAPI

Boot partition

Bootable floppy disk

Bus mastering

CD-ROM

Clustering

Command Queuing

Cylinder

Data transfer rate

DEFRAG

DMA

DVD

EIDE

Extended partition

Fast SCSI

Fast Wide SCSI

FAT

FAT32

FDISK

Floppy disk drive

FORMAT

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Keyword Definition

Fragmentation

Hard drives

Head

HVD SCSI

IDE

Low-level formatting

LVD

LUN

Magnetic Tape

Master drive

MSCDEX.EXE

NTFS

Partitioning

Primary partition

Principal of Electromagnetism.

Punch Card

RAID

RAID 0

RAID 1

RAID 2

RAID 3

RAID 4

RAID 5

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Keyword Definition

RAID 6

ScanDisk

SCSI

SCSI-1

SCSI-2

SCSI-3

SE SCSI

Sector

Slave drive

Track

Ultra SCSI

Ultra160 SCSI

Ultra160+ SCSI

Ultra2 SCSI

Ultra3 SCSI

Ultra320 SCSI

Wide SCSI

Wide Ultra SCSI

Wide Ultra2 SCSI

WORM

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Review Questions Chapter 7

1. How many drives can be connected to a floppy drive controller?

2. What is the best method of determining the number of drives available on a computer?

3. What are the three things to check when a floppy disk drive fails?

4. What is the best way to insure a long life for a floppy disk drive?

5. When you purchase a new floppy disk drive controller, what can you expect to get with it?

6. Other than physical size, what are the only differences between a 5¼” and a 3½” floppy disk?

7. What type of cable is used to connect a floppy drive to the external data bus?

8. What is the proper way to install a floppy disk drive cable?

9. You’ve received an error message that says “General Failure-Reading Drive A:” – What is the most likely problem?

10. Why is the voice coil actuator arm better than the stepper motor actuator arm?

11. What is hard drive geometry?

12. What is the best way to determine the geometry of an unknown drive?

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13. BIOS limits the number of heads to _______.

14. BIOS limits the number of cylinders to ________.

15. How many bytes of data does a sector hold?

16. What is the maximum number of sectors per track?

17. What does CHS stand for?

18. What is today’s standard hard drive?

19. When you install a new hard drive as a second drive, what must you set it at?

20. What is a partition? What are the two types?

21. Define a cluster.

22. How does the FAT work and what is it?

23. What is fragmentation?

24. How can you minimize the impact of a hard drive failure?

25. What is the function of ScanDisk?

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26. How do drive manufacturers overcoming the 528MB barrier?

27. How many devices can be installed on a SCSI-1 chain?

28. What is the effect of improper termination on a SCSI chain or device?

29. Sometimes the SCSI device driver conflicts with other drivers. What steps need to be taken to resolve the problem?

30. Name three advantages of using a CD-ROM driver.

31. What are the three steps to installing a CD-ROM?

32. Is a 16X CD-ROM 16 times faster than a 1X? Why?

33. How would you determine what type of CD-ROM to install in a computer?

34. Why would you use the MSCDEX.EXE real mode driver with Windows 95?

35. Instead of using a magnetic surface for storing data, a CD-ROM uses what type of technology?

36. What software is required for a CD-ROM installation?

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Chapter 8 – Buses

The success of the computer is due largely to its ability to expand and grow to meet the changing needs and/or economics of its user. In this chapter, we will be focusing on how to expand the motherboard to work with an ever-growing number of devices. We will also discuss conflicts within the computer – how they are both created, and reconciled.

Expansion Buses

Expansion buses are used to connect devices to the motherboard (via the data bus) and therefore allow the flow of data between that device and other devices in the computer. A bus is simply a channel over which information flows between two or more devices. Technically, however, if a bus connects only two devices, this is called a port. Early computers moved data between devices and the processor at about the same rate as the processor. As processor speeds increased, the movement of data on the bus became a bottleneck. Therefore, the design capability of the buses needed to evolve too. This lesson discusses that evolution.

Bus Functions

Most computers have at least four buses, which are located closer or further away from the processor, depending upon their function. A bus that needs to move information to and from the CPU the fastest would necessarily be located the closest to it. Similarly, the further away from the processor that a bus is located, the slower it is.

The following are common types of buses that are found on most systems today, listed in order of their speed.

• Processor Bus – This is the highest-level bus and is used to send information to and from the CPU.

• Cache Bus – Architectures, such as the Pentium Pro and Pentium II processors contain a dedicated bus for system cache.

• Memory Bus – This is the same thing as the processor bus, it connects the memory subsystem with the processor.

• Local I/O Bus – This is a high-speed bus that is used for connecting peripherals that need high-speed access to the CPU, such as video cards, hard drives, network cards, etc. Examples of this kind of bus are the VESA Local Bus and the PCI bus.

• Standard I/O Bus – This I/O bus is used for connecting devices that don’t require quite as much speed as the local bus, such as the mouse, modem, as well as compatibility with older devices. An ISA bus falls into this category.

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Development of the Expansion Bus

Every device in the computer (RAM, keyboard, network card, sound card, etc.) is connected to the external data bus. With expandability as the key focus for the personal computer market, a common method of attaching a vast array of devices to the motherboard is required. The common denominator for this problem is a standard connector that all device manufacturers can design to.

The solution is the development of the expansion bus. It serves two purposes. The first is to provide a common access point through a standard connector. The second is to provide a standard clock speed that is separate from the CPU clock speed. Apple resolved this problem by using the SCSI bus, but this was costly and not acceptable for the PC industry. To resolve this dilemma, the PC industry divided the external data bus into two parts, each with their own clock. This approach allows for the development of the CPU to be somewhat independent of the development of the expansion devices. The two buses are called the system bus and the expansion bus.

System bus - Supports the CPU, RAM and other motherboard components. The system bus runs at speeds that support the CPU.

Expansion bus - Supports any add-ons via the expansion slots and runs at speeds that support the peripherals.

Dividing the bus provides the best of both worlds. Upgrading a CPU requires changing the timing of the system bus while the existing expansion cards continue to run as before. Usually there is a jumper setting which will change the system clock speed to match the CPU. The ability for the motherboard to make this change sets the limit for the processor speed.

Let's now look at the development of the expansion bus. We will start with the first 8-bit bus and work our way to the new high-speed buses used today.

ISA (Industry Standard Architecture)

The PC bus was invented and patented by IBM. The original one was designed to work on the 8088-machine 8-bit bus architecture. Since processor speeds were not very fast, an expansion bus speed of 4.77 MHz was settled on. This was the standard bus on the XT computers. This 8-bit bus design was accepted as the industry standard and called ISA (Industry Standard Architecture). This bus, developed in 1981 by IBM, allows the manufacture of thousands of hardware expansion cards.

8-bit ISA Bus

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With the introduction of the 16-bit AT computers came the 16-bit ISA slot in 1984. Initially the 16-bit bus ran at 6, then 8 MHz. Finally, the industry agreed to an 8.33 MHz maximum speed. This expansion slot is just an extension of the earlier 8-bit slot. It is configured so that it will receive either an 8-bit or 16-bit expansion card.

16-bit ISA Bus

Note: The term ISA (Industry Standard Architecture) did not become official until 1990. Therefore, the 8-bit slot is called the XT and the 16-bit slot is called the AT.

When working with the modern computers of today, you will most likely encounter one or two 16-bit ISA slots. The 8-bit slot is, for all practical purposes, only found in very old computers. The16-bit ISA is still a mainstay in many new systems, but it does appear that it will be phased out of future technology. This will probably take more time than the industry believes because there are hundreds of millions of these buses out there and it will take some time before they completely disappear.

MCA (Micro Channel Architecture)

In 1986, the new 386 machines with their 32-bit architecture began to take over the market. While backward compatibility allowed the use of ISA 8- and 16-bit expansion cards, they did not take advantage of the power of these new processors. To respond to this change, IBM created a 32-bit expansion slot and called it MCA or Micro Channel Architecture.

The MCA bus did have several advantages over its predecessor. First, it was designed to meet the specifications of the new 32-bit architecture machines. It is faster than the ISA bus running at speeds of about 12 MHz. Perhaps the most impressive new feature of the MCA was its ability to self-configure devices. It was the predecessor of what we now call plug-n-play technology. While not totally plug-n-play, all configuration was accomplished automatically through software rather than setting jumpers or switches. Another feature introduced with the MCA bus is bus mastering. Any device connected to the bus could communicate directly with any other device on the bus. There were four types of MCA slots:

• 16-bit – standard design.

• 16-bit with video extensions – takes advantage of VGA circuitry to speed up video operations.

• 16-bit with memory-matched extensions – to support enhanced memory cards.

• 32-bit - for use with 32-bit processors.

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MCA Bus

With all its advantages, there were still some problems with MCA. The two most prominent were its lack of “open” design (required IBM licensing) and its lack of compatibility with other cards. Both of these affected the cost. In addition, its competitor EISA did not have these restrictions.

EISA (Enhanced Industry Standard Architecture)

Not to be outdone by IBM and mostly in response to the licensing issues, a committee of computer manufacturers developed an alternative to MCA. This alternative solution was called Enhanced ISA. EISA was released as an “open” design in 1988 and has all the improvements of MCA. Most importantly, it was less expensive.

Physically the EISA bus looks the same as the ISA (as far as size when looking down from the top). The difference is in the number of contacts and the depth of the slot. With close inspection, you can see a “double” set of contacts (one above the other). Both ISA and EISA cards can be used in these slots. When inserting an ISA card, the contacts on the card are restricted from reaching all the way to the lower set of contacts in the slot. EISA cards on the other hand have longer “fingers” and will reach all the way to the end of the slot thus allowing all the contacts to be made.

ISA & EISA Bus Top View

ISA & EISA Bus Cross Section

Local Buses

The use of ISA, EISA and MCA buses for most hardware applications worked quite well. However, as development of the personal computer progressed and with the introduction of graphical environments, the need for more speed increased. Compared to the increases in processor speed, the increases in expansion bus speeds fell well behind the pace. Processing the large amounts of video data to meet the needs of graphics interfaces, such

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as Windows, applications just could not tolerate the speed restrictions of the expansion bus. For example, a video card using an EISA bus running at 8.33 MHz was no match for a CPU external data bus running at 100 MHz. These high-speed systems needed to run at the speed of the processor.

One solution to the problem of video was to use co-processor cards. By installing a separate processor and memory on the video card, many of the problems could be resolved without ever using the expansion bus. You may have heard these cards called video accelerator cards. While this temporarily solved some of the video problems, it was not the answer. The answer was to tap into the CPU’s “local” bus for the high-speed requirements and still use the expansion bus for standard operations. Hence, the development of the local bus technology. This provided the best of both worlds, a standard low-speed bus to meet the needs of the installed base of existing expansion cards and a high-speed connection for video.

VESA (VL-Bus)

While the need for a faster bus design was important to many manufacturers, the video manufacturers needed a new design. In the early 90’s, video performance was a problem for most computers. Having to connect video cards through the 8.33 MHz expansion bus was a bottleneck to performance. The Video Electronics Standards Association (VESA) created a bus to deal with the need for faster video. One solution for increasing video speed was to install a co-processor on the video card. This processor reduced the workload on the main processor by handling standard issues like creating the windows in a Microsoft Windows environment. While this improved the performance by decreasing the amount of data to move, there was still a need to increase the speed of moving data between the main processor and the processor on the video board. The solution was to connect directly into the local bus that operates at a higher speed than the expansion bus.

The VL-Bus, or VLB for short, is not entirely a new design. It is actually designed as an extension of the popular ISA, 16-bit EISA slot and MCA. The EISA portion provides all the basic control functions (I/O addressing, IRQs, DMA, etc.). The VL portion provides the high-speed access. The increased speed provided by VL-Bus was very popular for both video and hard drive manufacturers.

With all of its advantages, came some disadvantages. It relied heavily on the design of the 486-processor bus. The introduction of the Pentium brought with it additional problems due to its high-speed capabilities. Running a VL-Bus at speeds greater than 33 MHz caused many problems. Only three VL-Bus cards could be installed in one system because of electrical loading. These problems were enough to limit the success of the VL-Bus to the 486 line of processors.

With the introduction of the PCI bus, VL-Bus technology has all but disappeared. Don’t expect to find it in anything other than a 486 machine.

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PCI

In 1992, Intel led a group of designers from IBM, Intel, DEC, NCR and Compaq who were intent on a solution for the limits of ISA, EISA and MCA bus designs. Using the same goals as the VESA group, this group designed the PCI bus (Peripheral Component Interconnect). The new bus was to provide a low-cost solution with high performance, automatic configuration and expandability. Their solution wasn’t an expansion of existing technology by tapping into the local bus, but the creation of a new bus. This new bus is sometimes called a mezzanine bus, as it resides between the CPU bus and the native expansion bus. The PCI bus incorporates a new set of controller chips that provide a bridge between the CPU, the PCI bus and the expansion bus. PCI is designed for operation with 32 and 64-bit systems and is the choice of Pentium platforms. It is considered standard equipment today. Most computers purchased today will have both PCI and ISA slots.

PCI owes its superior performance to several factors:

• Burst Mode – Burst is a term that is used in a number of technology contexts that refers to a specific amount of data being sent or received in one intermittent operation. This means that bits are sent in a “burst” instead of one at a time. When the PCI bus receives the initial addressing information, it can send multiple sets of data at a time.

• Bus Mastering – m Bus mastering is a way for the device to directly access memory without using the processor as a “middleman” to transfer the information. Devices that require high-speed data transfers benefit from this, and the processor is left free to complete other processes.

PCI 2.2

A PCI 2.2 card (64-bit, 66-MHz card) can be used in a 32-bit 33 MHz slot, 64-bit 33 MHz slot and a 64-bit 66 MHz slot.

PCI Expansion Slots

The PCI bus is capable of servicing more expansion slots that the VL-bus without any electrical problems that were common on the VL-bus (voltage drops from too many devices). Most PCI systems support three to four slots, although it is possible to have more. It should be noted however, that not all the slots are capable of bus mastering.

PCI slots are very common on today’s systems and we can expect them to remain so for at least the next several years.

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Summary of Bus Types

Type Width Bus Speed (MHz) Bus Bandwidth (MB/sec)

Bus Mastering

8 4.77 7.9 N ISA

16 8-10 15.9 N

MCA 16/32 10 20 Y

EISA 32 8 31.8 Y

AGP 32 66 254.3 Y

VL-Bus 32 33 127.2 Y

32 33 127.2 Y PCI

64 66 254.3 Y

Note: PCI, ISA and AGP are on almost every motherboard you will run into as a technician, but the others are still out there and you need to be knowledgeable of them as well.

USB

Another comer to the line of computer buses is called the Universal Serial Bus (USB). While not a bus in the sense of the previous buses, it is worthy of mention. It is a low to mid speed bus that can be used for a variety of peripherals, including mouse devices, keyboards, joysticks, scanners, audio devices and digital cameras, just to mention few. A USB can be either built into a motherboard or installed as an expansion card.

USB supports two data transfer protocols: synchronous and asynchronous. A synchronous connection transfers data at a guaranteed, fixed rate of delivery. This is required to support the demand of multimedia applications and devices. Asynchronous data can be transferred whenever there is no synchronous traffic on the bus. USB supports the following data transfer rates, depending on the amount of bus bandwidth a peripheral device requires:

• 1.5 Mbps (Megabits per second), for devices that do not require a large amount of bandwidth such as a mouse or keyboard.

• 12 Mbps synchronous transfer rate, for high-bandwidth devices such as modems, speakers, scanners, and monitors. A synchronous connection transfers data at a guaranteed, fixed rate of delivery. Guaranteed data delivery is required to support the demand of multimedia applications and devices.

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Most computers today have USB ports. The main reason for USB’s popularity is its true plug-and-play abilities. Devices can be connected easily using USB and started up without the need to re-boot the system (this is called “hot swapping”). Up to 127 devices can be chained together using USB and multiple devices can be connected to a single computer by using hubs, because it can supply power for the devices. USB devices only require a single IRQ if daisy chained. The maximum distance between USB devices is 5 meters.

Although it was slow in coming, USB has gained industry acceptance and most new systems sold today have at least one USB port. In addition, many devices are being created to take advantage of this technology.

Note: Windows 95 does not support plug-n-play unless specifically stated.

USB Port

USB 2.0

USB 2.0 offers a third speed of 480 Mbps that exceeds standard FireWire speeds. USB 2.0 is also backward compatible with standard USB.

FireWire (IEEE-1394)

The IEEE-1394, a "new" high-speed interface that has been around for many years, is not truly a bus. We are mentioning it here however, because it works in a very similar way to USB (only much faster). Originally, Apple developed a product using this technology called FireWire, and Sony has a product called i-Link.

IEEE-1394 is defined as part of the SCSI-3 family of standards and it supports dozens of devices in a chain, hot swapping, and plug and play, but it does it at speeds of up to 400 Mbps, as opposed to USBs 12 Mbps. Although this technology hasn’t taken off like expected in the storage device industry, it has become very popular in several specialty markets, such as digital video.

AMR (Audio/Modem Riser)

This Intel 46 pin riser card contains both audio and modem functionality. These cards allow the manufacturer to more quickly certify their equipment or add more functionality to an existing board.

CNR (Communications and Networking Riser)

The CNR is the proper evolution of the AMR cards. These cards provide audio, modem, and networking functionality. Intel also manufactures them.

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AMR and CNR

AGP (Accelerated Graphics Port)

Intel developed the AGP (Accelerated Graphics Port) in response to a need for more bandwidth between the processor and the video subsystem. Today’s graphic intensive applications and Internet Web sites were pushing the limits of what the PCI bus can deliver. In addition, a growing trend towards 3D acceleration and full-motion video made a new technology necessary.

AGP allows the video processor to access the main system memory directly (this is known as video pipelining). The interface is only between these two devices (hence, it is a port and not a bus), and is much more efficient. Because AGP is a port, it is not expandable. It is simply an interface between video and memory. You will find this brown port on newer motherboards and it is a bit smaller than the white PCI slot.

This technology first came out in 1997 in Intel’s 440LX Pentium II chipset. This technology negates the need for an expensive 3D video card, and is becoming necessary for people who work in graphic-intensive environments.

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The AGP interface is physically similar in size and shape to the PCI slot, but is located closer to the processor and further from the edge on a motherboard. It includes speeds of 66 MHz, is 32-bits wide, and runs at full bus speed, which means that it has doubled the speed of the PCI technology.

In order to take advantage of AGP a computer will need the following:

• AGP Video Card

• AGP Chipset Motherboard

• Operating System Support

• Driver Support

Here’s a chart spelling out the different AGP standards:

AGP Standard Data Transfer Rate

1x 264 MBps

2x 528 MBps

4x 1 GBps

8x 2 GBps

Configuring Expansion Cards

The purpose of these buses is to connect devices to the motherboard by installing an expansion card. As we learned in another section, the external data bus (that the expansion buses connect to) is simply a large party line. All devices are connected to the same communication bus. This configuration presents two problems. First, the CPU must know how to contact each device on the bus and second, it must be able to control which device is allowed to read or write data to the bus. Lets first start by looking at addresses.

Addressing – Where is that card?

The bus system establishes a connection between the CPU and the expansion devices, and provides a path for the flow of data. A means of controlling that expansion device is talking and which is listening is required; otherwise, there would be complete chaos. We have discussed the data bus in terms of how many bits or bytes of data can be sent at one time. Actually, many more wires make up the bus other than the ones used for data. Some of these extra wires are used to assign a unique I/O Address to each device. Everything in a computer, whether hardware or software, requires a unique name and address, otherwise the CPU could not keep track of what is going on. I/O addresses are binary numbers placed by the CPU on specific wires on the bus. They are actually a range of numbers that are assigned to a single device. Each device will monitor its

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assigned range of numbers and when the CPU places one of them on the bus, it will recognize the number and respond accordingly. Any numbers not assigned to the device will be ignored. This range of numbers is actually a set of commands that the CPU uses to communicate with an individual device. Memory mapped I/O is a specific type of I/O that can be used in some instances. Memory mapped I/O uses memory locations to communicate with peripherals.

The important thing to remember about I/O addresses is that no two devices can have the same range of numbers or even an overlap of numbers. If this were to happen, a conflict would exist and the system would crash or lockup. The following table lists address assignments for an XT and an AT computer.

COMMON I/O PORT ADDRESS ASSIGNMENTS

PC/XT PORT USED BY PC/XT PORT USED BY

000h-00Fh DMA CHIP 8237A 2E8h-2F7h COM4

020h-021h PIC 8259A 2F8h-2FFh COM2

040h-043h PIT 8253 300h-31Fh PROTOTYPE ADAPTER

060h-063h PPI 8255 320h-32fh HARD DISK CONTROLLER

080h-083h DMA PAGE REGISTER 378h-37fh LPT1

0A0h-0AFh NMI MASK REGISTER 380h-38fh SDLC ADAPTER

0C0h-0CFfh RESERVED 3A0h-3AFh RESERVED

0E0h-0EFfh RESERVED 3B0h-3BFfh MONOCHROME ADAPTER/PARALLEL INTERFACE

170h-177h SECONDARY IDE CHANNEL

3C0h-3CFh EGA

1F0h-1F7h PRIMARY IDE CHANNEL

3D0h-3DFfh CGA

200h-20Fh GAME ADAPTER 3E8h-3E7h COM3

210h-217h EXTENSION UNIT 3F0h-3F7h FLOPPY DISK CONTROLLER

220h-24Fh RESERVED 3F8h-3FFh COM1

278h-27Fh LPT2 C000-C7FF VGA VIDEO CARD

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I/O address numbering conventions:

• I/O addresses are 16-bit addresses and displayed with a hexadecimal number.

• By convention, the lead “0” is dropped.

• Hexadecimal I/O addresses are case sensitive (must be capitals).

As previously shown, all devices must have a unique I/O address. For consistency, the most common devices have preset I/O addresses and cannot be changed. With these devices, the default setting will work and you will not have to configure the address.

For all devices that are not preset, read the documentation that comes with them. It will explain how to set the I/O address and define the limits for that device. Normally, all that is required is changing jumpers or switches. Some cards will provide software for configuration of I/O addresses. Be sure to check the documentation provided with the card or device. The newer plug-n-play devices will be configured by the operating system when installed.

Note: Just like shortening the 4-digit address number, I/O addresses are usually referred to by the first three digits of the range.

I/O address conflicts do not create themselves. Once set, it is highly unlikely that they will change without some intervention by an operator. Anytime there is a conflict and either of the devices activates, both devices will fail. In the worst case, the computer locks up. Generally, an I/O conflict will occur immediately or shortly after the installation of a new hardware device. Therefore, the best way to prevent I/O address overlaps is to document all I/O addresses.

Many commercially available programs will check ALL of the I/O addresses for every device on your computer. You can also use MSD (Microsoft Diagnostics), a program provided with DOS.

If you use Windows 9x or the Windows NT operating system, you can use the Device Manager to locate and resolve IRQ and address conflicts.

Interrupting – Who’s Turn to talk?

We have seen how the CPU uses the I/O address to send instructions to the devices in the computer. We have also seen that the external data bus is a party line. The problem is how does the CPU know when a device needs its attention. It works the same way that a student would get the attention of the instructor. Each device will raise its hand and wait for the instructor to respond. Electronically, each device will use a hardware interrupt. These hardware interrupts are no more than a wire that is assigned to the device. These wires are either connected directly to a standard device such as a keyboard or system timer or connected to the bus slots making them available to any device installed in the slot. When the device needs the attention of the CPU, it places a voltage on the wire. The CPU programming will then recognize the interrupt and respond to the device via the I/O address for that device. As simple as this sounds, it is actually more complicated.

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First, the CPU has only one wire designated as an interrupt wire so it must rely on another chip to intercept the interrupts and communicate the status to it. Second, computer buses are designed with a limited number of interrupt wires as part of the bus system.

The solution to these problems is the addition of an interrupt controller chip and a limit to the number of devices that can be connected to the motherboard. The interrupt controller is known as an Intel 8259 and allows for up to eight interrupts. This was no problem with early computers because there were very few devices available for the bus slots. As time moved forward, and with the addition of sound cards, modems, scanners, etc., this limit became a problem. Let’s now take a look at the 8259, how it works and how to deal with the issues of limits.

8-bit bus

The early 8088 computers with the 8-bit bus used only one 8259 chip. This limited them to only eight available IRQs. Since a keyboard and a system timer were a fixed part of all computers, these IRQs were permanently wired in the motherboard. The remaining six wires were then made part of the expansion bus and were available for any other devices. Note that the eight IRQs are numbered 0 thru 7.

8259 Chip with IRQ Assignments

16-bit bus

With the introduction of the 286 processor and motherboards, an additional 8259 was added to the circuitry. This made16 interrupts available. However, these two chips needed to be connected together so they could work as one. The CPU still has only one interrupt connection. To resolve this problem, the output of the second chip is connected to IRQ2 on the first chip and any interrupts formerly on IRQ2 are routed to IRQ9 (second IRQ of second chip). This combined IRQ is often called 2/9. From the introduction of the 286, to the present day computers, there are 15 available IRQs. This technique of connecting 8259 chips is called cascading and continues today.

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Cascading 8259s

The following summarizes the requirements of cascading 8259 IRQs chips.

• IRQ 2 and IRQ 9 are the same IRQ (in that 2 is cascaded to 9 for access up to 15).

• Three IRQs are hard wired (0,1 and 8).

• Four IRQs are have become de-facto standards (6,13,14,15).

• Four IRQs are default settings, but can be changed (IRQ 3,4,5 and 7).

If you go looking for the 8259 chips on a modern motherboard, you will not be able to find them. They have become integrated as part of the CPU chipset.

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The following table shows typical IRQ assignments:

Typical IRQ Assignments

IRQ Function Bus Connection

IRQ 0 System Timer NO

IRQ 1 Keyboard Controller NO

IRQ 2 Cascade from 9 NO

IRQ 3 COM2, COM4 YES

IRQ 4 COM1, COM3 YES

IRQ 5 LPT2 YES

IRQ 6 Floppy Controller YES

IRQ 7 LPT1 YES

IRQ 8 Real-Time Clock NO

IRQ 9 Available (IRQ 2) YES

IRQ 10 Available YES

IRQ 11 SCSI/Available YES

IRQ 12 Mouse/Available YES

IRQ 13 Math- Coprocessor/If no processor available

NO

IRQ 14 Primary IDE Controller YES

IRQ 15 Secondary IDE Controller YES

Note: IRQ settings are a large part of the A+ core exam.

Configuring IRQs

Devices lacking a fixed or standard IRQ must have their IRQ set during installation. Read the accompanying documentation to learn about the setting for the particular device. The documentation will tell not only how to set the IRQ, but also any limits of the device. IRQs are configured via jumpers, switches, software drivers or automatically as in Windows 9x and Windows 2000 Plug-And-Play.

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Some devices have a limited number of IRQ settings and you may need to change the IRQs of other devices in order to free one of these IRQs. For instance, if a customer recently installed a sound card that locks up when a parallel port tape backup is used on the system, there is probably an IRQ conflict. Check the sound card and the tape backup IRQ settings and change one if needed.

In the Windows 9x operating system, the device manager will identify any hardware conflicts should one be assigned incorrectly.

IRQ Conflicts

IRQs are limited and no two devices can have the same IRQ assignment. If two devices have the same IRQ, the CPU will not know which one to respond to and will become confused, leading to a system halt. Perhaps the most common problem encountered after installing a new device is an IRQ conflict. This will be immediately noticed as either the devices or the entire system will lock-up. Newly installed sound cards are notorious for IRQ problems.

Note: CMOS configured IRQs happen before plug-and-play configured IRQs.

Another common source of IRQ conflicts is devices using communication ports. As you may have noticed, COM1 and COM3 are assigned IRQ4 and COM2 and COM4 are assigned IRQ3. This assignment actually works as long as the device on COM1/3 or COM2/4 are never used at the same time. If you need more than two COM ports, you will need to assign different IRQs to COM3 and COM4.

DMA Channels

In addition to configuration of the IRQ, a less common and similar configuration will cause the same problems as IRQ conflicts. This is called DMA or Direct Memory Access. High-speed communication devices use direct memory access. It is used to move data directly between the device and memory without having to be managed by the CPU, thus speeding up the process. These devices need to move large amounts of data very fast. Devices such as sound cards and SCSI adapters (PCI, VL-BUS or EISA) are examples of devices that will use DMA. Working with DMA is similar to working with IRQs. There are only two differences, the chip used is an Intel 8237 and not all devices need DMA. This is good because the 8237 controller will handle only four channels. Like the 8259, 8-bit computers used one DMA chip and 16-bit computers and newer used two DMA chips that are cascaded. The 0/4 channels are connected. So, AT computers have 4 DMA channels and ATX computers have eight DMA channels.

The only standard DMA channel is channel 2. It is assigned to the floppy disk controller. Channels 0-3 are used for 8-bit transfers and 5-7 for 16-bit transfers.

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DMA Channel Assignments

DMA Channel Function

0 Cascade from 4

1 8-bit sound card/Available

2 Floppy Controller

3 ECP Parallel/Available

4 1st DMA Controller/Available

5 16-bit sound card/ Available

6 SCSI/Available

7 Available

Assigning Resources through Ports

Computer resources are a precious commodity. We have seen that every device needs a unique I/O address and a unique IRQ. Being able to properly assign these resources has been a problem for a long time. To simplify the installation of serial communication devices and parallel communication devices, IBM created preset combinations of IRQs and I/O addresses. These connections are called ports since they provide a two-way communication path out of, and in to, a computer. Rather than having to remember the I/O address or the IRQ, all you had to do was assign an available port. Serial communications are assigned to COM1 thru COM4 (COM – communication) and parallel communications are assigned LPT1 and LPT2 (LPT – Line Printer). The following table shows the standard settings for COM and LPT ports. For the A+ exam, you may want to memorize these settings.

Standard Ports

Port COM1 COM2 COM3 COM4 LPT1 LPT2

IRQ 4 3 4 3 7 5

ADDRESS 3F8h 2F8h 3E8h 2E8h 378h 278h

Note: For the A+ exam, you will probably encounter several questions on standard IRQ, I/O address and DMA settings. Making sure that you know these standard settings; it might earn you a couple of extra points!

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Remember the shortage of IRQs in the pre-286 computers? Because of this, IBM doubled up on the IRQs for the COM ports. At that time, this worked well. First, very few devices could be used on COM ports so the likelihood of using more than two was slim. Second, as long as the two devices used were not operating at the same time, there would be no problem. Since DOS couldn’t do two things at the same time, this too was a highly unlikely event. However, times have changed and there are hundreds of devices available and with operating systems like Windows, it is possible to have several modems running at the same time. Any time you use more than two devices and need to assign COM ports, you will have to find some additional free IRQs and assign them appropriately. Early LPT ports did not actually need an IRQ so IRQ 5 and 7 were usually available. Early printers were not bi-directional for this reason. That is, they did not have to communicate back to the CPU or software; therefore, they did not need permission to talk. Today’s printers do use bi-directional communication so you will have to be careful with assignment of these interrupts.

Most computers are manufactured with built-in ports and have cable connections available either directly off the motherboard or in an expansion slot. In this case, the standard ports are assigned to them. This makes for easy installation of an external device by simply plugging in the port and assigning it to the device. If necessary, these ports can be disabled (by using CMOS setup) and therefore freeing their I/O addresses and IRQs for another device. An example would be when installing a new internal modem on a machine with two external serial ports on the motherboard. By disabling one of these ports, its address and IRQ are now available for the internal device. Simply assign the device to the now free port.

Conflicts with PORTS

Lets say that you have decided to update your computer and add a sound card. You install the sound card and there don’t seem to be any problems until you try to play a new CD to see how well the audio works. As soon as the CD starts, your mouse stops. You are able to use the keyboard shortcut keys to exit the program and reboot. Once again, everything works fine until you start the CD. What could the problem be?

It may be obvious that you have a conflict between your mouse and your CD. Right? Wrong! The problem started when you installed the sound card, not the CD. The most likely problem is that you are using a serial mouse and it is assigned the same IRQ as the new audio card. Any time that a conflict suddenly arises, always look for a newly installed card and check for IRQ and address conflicts. To resolve this problem, you will most likely have to change the IRQ on the sound card.

Installing an Expansion Card

Installing expansion cards is a common task of a computer technician. It is actually quite simple as long as you follow four basic guidelines.

The guidelines for installing expansion cards are simple:

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• Make sure that you have an available expansion slot and that the card you purchased matches the available slot.

• Power off the PC and take the proper ESD precautions

• Read the documentation.

• Keep the IRQs, DMAs and I/O unique.

• Document; Document; Document!

If good documentation is not available, some good support programs might help. A good IRQ and I/O Address tester is CheckIt Pro from Touchstone.

With Windows 9x and W2k comes “Plug and Play. PNP cards need only be physically installed and the computer turned ON. Windows will find the card and guide you through the set up. Most of the time this works, however, a good Computer Professional will keep track of the IRQ, DMA and I/O address. Windows 9x hardware properties also do a good job of identifying (and allowing changes) of these settings. To find properties, go to the explorer program and right click on “My Computer”. From the menu in “My Computer,” select “Properties” and then “Device Manager.” A good way to document a computer is to print a complete list of the computer’s hardware settings from this property dialog box.

Note: For PNP to work, the computer must have a PNP BIOS, which keeps a list of used system resources, the operating system must be PNP compliant and the device card must be PNP compliant.

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Summary

While this is a short chapter, the information provided is very important. Installing expansion cards and peripheral devices will be a major part of being a computer technician. In addition, the number one reason for hardware conflicts is generally caused by an IRQ or I/O address conflict. The following summarizes the key points of this chapter:

• Expansion buses are the means of connecting devices to the motherboard.

• Expansion buses have changed to keep up with the speed of processors.

• A computer technician must know how to identify the various expansion buses to insure compatibility and maximize performance when upgrading a computer.

• Everything in a computer needs a unique address.

• In order for the CPU to identify what devices need to use the data bus, it monitors the IRQs.

• No two devices can use the same IRQ or DMA channel.

• Most conflicts after an installation of a new device are caused by IRQ conflicts.

• Ports (COM and LPT) are used to simplify the installation of common devices such as printers and modems.

• A port is a pre-assigned combination of an I/O address and IRQ.

• ISA, MCA, EISA, VESA VL-Bus, PCI, USB and AGP are the different types of bus architectures.

• In order for a CPU to keep track of it’s devices and communicate with them, unique individual I/O addresses must be assigned to each device.

• In order to prevent devices from all “talking” to the CPU at the same time an IRQ (Interrupt Request) number is assigned to devices that inform the CPU which device is requesting its attention. You should memorize as many of the typical IRQ assignments as you can.

• The DMA (Direct Memory Access) moves data. It handles all the data passing from peripherals to RAM and vice versa.

• COM ports are used for serial devices (modems, etc.) and LPT ports are used for parallel devices (printers, etc.) to give these devices direct communication with the CPU and to make installation easier.

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KEYWORDS Exercise

Define each of the following keywords. Hint: There’s a glossary in the back of this book.

Keyword Definition

AGP

Burst Mode

Bus Mastering

DMA

EISA

Expansion bus

IEEE-1394

Interrupts

ISA

MCA

PCI

System bus

USB

VESA

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Review Questions Chapter 8

1. Why does a computer need an expansion bus?

2. Name the five available expansion buses.

3. What happens if two devices use the same I/O address?

4. How many IRQs are available?

5. Under what conditions would a second modem, installed and assigned to COM3, work?

6. Name the two parts that the external data bus is divided into and the purpose of each.

7. What is the standard that governs computer buses?

8. What is the difference between ISA and EISA cards?

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9. Why was VESA created?

10. How is the PCI bus better than previous technologies?

11. How does the CPU use I/O addresses?

12. What is the I/O port address of COM2?

13. What are the functions of IRQs?

14. List as many of the standard IRQ assignments as you can.

15. What is the function of the DMA chip?

16. Why is it important not to assign the same IRQs to more than one device?

17. What is the difference between COM ports and LPT ports?

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18. Why is it important to document IRQs, DMAs, and I/O addresses?

19. Which bus supports hot swapping?

20. FireWire is based on the _____________ standard.

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Chapter 9 – Disassembly, Reassembly, and Upgrading

There is no way around it, if you are going to be a computer technician, you will have to know how to disassemble and reassemble a computer. One of the main tasks that a Computer Professional will repeatedly encounter is upgrading an existing system. This chapter is all about taking apart and putting a computer back together.

Disassembly and Re-assembly of a Computer

One task that a Computer Technician is constantly involved in, is upgrading. With new technology coming out every day, we are in a constant struggle to stay current. However, before beginning the process of repairing or upgrading a computer, it first must be disassembled. This is obviously the first step in repairing a computer and a thorough understanding of how to take one apart (and put it back together) is a requirement of the Computer Professional. This section will establish guidelines for successful disassembly, upgrading and re-assembly of a computer. It covers the tools and practices required of a Computer Technician to physically take a computer apart and successfully put it back together. Although this section will mention software that a Computer Technician should have and know how to use, the detailed use of software is covered in another lesson.

Preparation

Preparation is the main ingredient to a successful, efficient and profitable repair or upgrade. Before attempting any work on a computer, it is wise to know what you are working with and have a good understanding of the problem, or task, at hand. Ten minutes or even an hour in preparation can save hours of endless guessing and frustration. Documentation is the key to preparation. If adequate documentation is not readily available, collect it or make it. When you finish a job, don’t forget to save the documentation including what you did and any problems encountered. The following lists some examples of the types of documentation that should be available and some questions that should be considered before the job starts.

Documentation to collect before starting the job:

The following list provides examples of the types of documentation that should be available before you begin a repair.

• Make or find a list of the current configuration of the computer. This will include make and model of drives and peripherals and a list of their IRQs, I/O addresses and DMA channel assignments.

• Copies of the computer and/or motherboard documentation.

• List of all installed expansion cards. If possible, include when they were originally installed.

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• Copies of documentation for the operating system (especially if you are not familiar with this system).

• A plan of action. Writing down a plan of action before starting a project will often keep you focused and on target. Remember, plans can always be changed, but without a plan, you may wander aimlessly through the project and even get sidetracked or lost.

Questions to ask yourself before starting the job:

Carefully consider the following questions before you open the case of any computer.

• Why am I taking this apart?

• Do I have everything necessary to do the job?

• Do I need more information before starting this job?

• Are there any components of this machine that may be proprietary hardware? If so, do I have the right tools and parts to do the job?

• Do I have all the tools and parts to complete the job?

Tool Kit

A Computer Professional does not need a large toolbox, as a computer only requires a few basic hand tools and a handful of diskettes to resolve most problems. Be careful when working on a proprietary machine, as special tools are often required. Often a small canvas bag or a brief case will be sufficient to carry everything required. The following includes a minimum of hand tools and software that will meet most needs.

Screwdrivers One large and one small flathead (regular) and Philips-head (sometimes called a cross). Stay away from magnetic screwdrivers. They are convenient for picking up lost screws, but being magnetic, they could cause other problems if laid in the wrong place.

A Torx Driver These are used to remove those oddball star shaped screws found on some of the proprietary computers. (Sizes T-10 and T-15)

Tweezers Very convenient for picking up lost small parts (screws). You might consider long and plastic (won’t short out anything).

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Needle-nose Pliers They can be used to pick up dropped items and to hold or loosen things.

Chip Removers (Optional) These are very useful when changing video RAM, or other (older) RAM chips, that are pushed into a socket.

Tube for Small Parts

A short plastic tube (with caps on both ends) will keep those loose screws and small parts from wandering.

Compressed Air A can of compressed air is helpful to remove dust.

ESD Tools An anti-static wristband is necessary. Anti-static mats and anti-static bags are helpful.

Multi-meter A small digital type that is capable of measuring volts (AC and DC) and ohms (resistance or continuity) is all that is needed.

Flash Light A small (bright) light for seeing in those hard to get places.

Nut Driver Set Sizes 3/16”, 7/32”, and ¼.”

Curved Hemostats Good for picking up and holding small parts. Straight hemostats will work most of the time, however, the curved ones will get into those small places that the straight one won’t. Having a set of both wouldn’t hurt.

Many computer stores sell small tool kits for repairing computers. If you are a beginner, one of these kits will suffice, but should be considered a minimum requirement. With time, you will be able to build your own customized tool kit.

Software:

Software is a key component of any tool kit. What you need is highly dependent on the operating system with which you will be working. At the very least, you will need a bootable floppy disk (one for each operating system - version of DOS, Windows 95, Windows 98, Windows NT, Windows 2000, Linux, etc.).

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Operating System Disk:

Make sure copies of the original operating system disks (or CD) are available. If it becomes necessary to install one or more components that were left out during the original installation, the computer may require verification of serial numbers (the original disk #1) before allowing any additional files to be installed.

Software Utilities:

There are many good quality utility programs available on the market today. These programs will allow an experienced user to find and correct many problems. However, caution should be used when “correcting” a problem that the software identified. The software may consider something as a problem simply because it does not recognize it. In some cases, correcting the problem can cause even worse problems than those you had when you started. As a Computer Professional, you are far better off to master one good software system than to have a box full of ones that you don’t know how to run effectively. Don’t forget DOS. DOS is full of commands that are usually forgotten or never used.

WARNING! Older versions of utility programs are designed to work with DOS and Windows 3.x. They can wreak havoc on a Windows 95/98 or later system.

Disassembly

Disassembly of a computer is a very simple process. However, since there are many manufactures, each seeking their own unique marketing identity, each brand will have some custom components or a custom layout. The best strategy for an efficient disassembly is to locate and use the manual that came with the computer. Often manuals don’t give a lot of technical information, but they are usually good about how to remove the cover. The following procedure will help establish a routine for efficient disassembly of most computers:

Starting points:

• Make a complete backup of necessary operating system and working files.

• Document the system (hardware and software).

• Create a clean workspace with plenty of room.

• Gather all the necessary tools for the job.

• IMPLEMENT SAFETY FEATURES.

• Turn OFF the computer.

• Disconnect the power cables.

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• Put ON anti-static wrist strap.

• Locate screws for the cover - check the manual for location (sides or back).

• Remove screws. It’s a good idea to have a box or plastic tube to keep them from being lost.

• Remove the cover.

• Document location of expansion cards and drives.

• Remove all of the cards and place them in anti-static bags (note screw on end tab of the card).

• Document the location and connections for each drive (pay special attention to the red wire on the data cables - this notes “pin one” on the device and driver).

• Remove the cables (power supply and data).

• Remove the drives from their appropriate bays - look for screws on sides (check the manual).

• Remove the motherboard.

Re-assembly

Re-assembly follows the same procedures as disassembly, but in the reverse order. When installing components, remember the following:

• Do not force connectors into place - if they don’t fit easily, they are probably in the wrong place.

• Expansion cards may require some force, or side-to-side movement to get into location, but do not force.

• When removing cables, remember the pin # 1 locations. Check notations on the circuit boards and look for the red wire on the ribbon cables.

• Connect the cables to the drives before installing them in the bays.

• Test the system before replacing the cover.

Upgrading a Computer

In today’s world of constant change, the number one activity of a Computer Professional is upgrading old systems to the latest technologies. The concept of upgrading a computer is based on the ability to expand and update, therefore getting longer life and more utility out of one system. However, a simple software installation can sometimes lead to

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hardware conflicts, and the need for an upgrade, as computer owners try to squeeze one more year out of “old faithful.”

Before you begin to upgrade any computer, you need to document the system. You should create and maintain files on all computers for which you are responsible. You can use any word processor, spreadsheet or even a database to create a form to maintain your records. Each form should contain all the specifications for every component on the computer. It should be as detailed as possible.

The Number One Question!

Does it have enough memory? This is the question asked most frequently before an upgrade to a computer is considered. As programs and hardware get faster, and are required to do more graphics and animation, the need for memory is as important as the need for speed.

Memory upgrades are perhaps the simplest to perform, but can be very confusing without prior planning. Purchasing the right memory to do the job is more than half the process of the installation. Before installing memory, there are several things to consider:

• Memory chip format (DIPP, SIMM, DIMM).

• Banking requirements – width of the data bus and type of memory module determines how many modules will be required.

• Number of free memory slots – if all the slots are full, you will have to replace the existing modules with larger ones. For example, if you have 16MB and want to upgrade to 32MB you will have to replace the existing modules with 32MB since you can’t add to the 16MB.

• Memory Speed

• Type of RAM needed - Standard DRAM or EDO RAM, etc.

• Parity

• EDO or no EDO – you cannot mix EDO memory and non-EDO memory. If your system already has EDO, you must add EDO, etc.

The best source of information, to check before obtaining memory, is the documentation that comes with the computer (motherboard). This source will generally list the type of memory required, how many SIMMs are required and their location on the motherboard. If this information is not available, open the case and look. Some documentation will even provide a chart that tells exactly what memory is already there and what is needed to upgrade to a given level.

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Memory Configurations

Onboard Bank 0 Bank 1 Total

8 MB 8 MB

8 MB 4 MB 4 MB 16 MB

8 MB 8 MB 8 MB 24 MB

8 MB 16 MB 16 MB 40 MB

8 MB 32 MB 32 MB 72 MB

DISABLED 64 MB 64 MB 128 MB

The various memory formats and installation of SIMM modules is discussed in detail in the chapter on Storage Devices – Memory. This particular chart was from an early Pentium computer. Today, upgrading memory is as simple as determining the type needed and installing it in the slots provided.

CPU Upgrades

Installing a new CPU is one of the easiest ways of adding new life to a computer. In many cases, it is as simple as removing the old one and inserting the new one. The number one question to ask is can the CPU be upgraded and to what? The answer to this question is in the motherboard. The motherboard must have the appropriate socket, data bus, address bus, and crystal to support the new CPU. Consult the documentation that comes with the motherboard. This documentation usually contains a table that will define what CPUs can be installed. If the upgrade is going from one level of the same family of CPUs to another, there is usually no problem. If, on the other hand, you want to upgrade a 386 to a Pentium, then a new motherboard is the only answer.

A General procedure for installing a CPU:

• Turn off the computer and unplug the power cord.

• Disconnect external devices (AC power and monitor power).

• Follow the appropriate ESD safety procedures.

• Remove the cover.

• Locate the socket for the CPU. It may be on the motherboard or on a removable processor card.

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• Remove the old processor. This may require special tools for older processors. The newer Pentiums usually have a ZIF socket (zero insertion force). Move the handle to the upright position to open the ZIF socket (this should not require force). The CPU can then be easily removed.

• Install the new processor. Be certain to align the chip properly (this is critical). Look for a key pinhole in one corner, a blunt edge on one corner of the socket, a corner with a pin arrangement, which differs from the others or some other identifying mark. Align this mark with the corner of the socket, which contains a blunt edge. Secure the ZIF handle. Check the documentation.

• Set any jumpers or switches on the motherboard. Check the documentation.

• Replace the cover and power up the computer.

• Some computers may require CMOS setup changes.

Upgrading of some CPUs may also require the installation of a new voltage regulator and/or cooling fan. Be sure to check the motherboard and CPU documentation. Failure to install these parts with the new CPU will destroy the CPU.

Expansion Cards

Just like installing memory, the installation of expansion cards is a common upgrade practice. The addition of expansion cards is a means of adding many peripheral devices such as modems, networks, scanners and sound cards. Before installing (or purchasing) an expansion card, it is a good idea to make sure that it will work in the system to be upgraded.

Ask these questions first:

• Are there any available expansion slots?

• Will the card in question fit in the type of slot available? Does it match the bus type of the motherboard?

• Are there any available I/Os and IRQs in the system? If so write them down.

• Is there enough memory (RAM and hard disk space) available to run the device and its software?

• Does the card require a DMA channel? If so is one available?

• What are the potential conflicts with other cards and devices?

• Will the operating system support this card? If so, are all the necessary drives either provided with the operating system or will they have to be provided with the card?

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After determining that the expansion card will work, the installation is a simple three-step process:

• Set any jumpers or switches for IRQ and I/O addresses.

• Install the card and cables.

• Install any software for the card.

The first step (IRQ and I/O setup) is perhaps the most confusing and frustrating part. This is especially true if the computer is not properly documented.

Note: Be sure not to leave any slots without their cover. A missing expansion slot cover can cause a computer to overheat.

General procedure for installing an expansion card (non Plug and Play):

• Read the documentation that comes with the card and note any special requirements or limitations, before you start the installation.

• Check the computer documentation (run MSD or other diagnostic program) and determine what IRQs and I/O addresses are available.

• Configure any jumpers or switches on the card.

Note - Some cards may require changes in order to prevent conflicts and insure that all devices work.

Switches

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Jumpers

• Turn off the computer and unplug the power cord.

• Follow the appropriate ESD safety procedures.

• Remove the cover.

• Install the card in a free slot. Power up the computer, note any conflicts and make adjustments as necessary. Remember to remove power and use ESD precautions when making changes

Installing an Expansion Card

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• Replace the cover.

• Install any software drivers or applications.

General procedure for installing an expansion card (Plug and Play)

The latest technology available for installing expansion cards is called “plug and play.” This is an independent set of specifications developed by a group of hardware and software companies. The purpose of this specification is to enable the user to make configuration changes with minimal intervention. Installation of a plug and play device should go like this - physically install the card, turn the computer ON and use the device. Macintosh has used the plug and play concept for a long time.

In order for plug and play to work, the device must be able to identify itself, and its system requirements, to the system. The operating system will then set the device and make any other adjustments (reconfigure other devices as required). When installing a PNP device, you must be sure of three things:

• The computer hardware (motherboard, BIOS, etc.) is PNP compliant.

• The operating system is PNP compliant.

• The device is PNP compliant.

If any of these conditions do not exist, PNP will not work. Hint - if a device is Windows 95/98 compliant, it is PNP.

Note: Windows NT is not plug and play compatible, but the new Windows 2000 is. For helpful technical support for Microsoft products, visit their technical support information Web site at http://search.support.microsoft.com. This searchable database offers a wealth of information to the Computer Professional.

Drives

Installing a new drive is not difficult, however, a few things must be considered before purchasing a new drive:

• Will the drive physically fit inside the computer? Some desktop cases only have enough space for one hard drive, or the available space may be occupied by another device (CD or floppy).

• Will the computer’s BIOS and operating system support the size (storage MB capacity) of the drive?

• Will the drive controller support the new drive? A second or updated controller may be required.

• Are there sufficient cables (data and power) to install the drive?

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Procedure for installing an IDE drive:

Installing an IDE drive will require some preparation of the hardware as well as the software necessary to get it running properly. Hardware preparation includes ensuring that you have the correct drive, a place to physically install it, and the proper cables to connect it. The software preparation includes at least a bootable DOS disk with a minimum of FORMAT and FDISK. A Windows 95/98 startup disk will do the job. If you don’t already have such a disk, be sure to make one before removing the old drive. Follow these steps to install the drive:

• Collect all the necessary documentation for the drive and the computer.

• Turn off the computer and unplug the power cord.

• Follow the appropriate ESD safety procedures.

• Remove the cover.

• Set the jumper for the drive. Consult the documentation that came with the drive. It must be set to single use, master or slave. If this is a second drive, both drives may require jumper settings.

• Connect the cable to the drives. The end connector should be plugged into the master drive. Be sure the cable orientation is correct (pin # 1 to the red wire).

• Connect the power cable

Cable Connections

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• Install the drive into its bay.

Note - it may be advisable to set up and test the drive before final installation in the bay.

• Re-connect the power, boot the computer and run the CMOS setup utility. The CMOS must be set to recognize the new drive. See the manufacturer’s documentation for proper CHS configuration (don’t forget that drives larger than 528 MB (approximate) will require LBA to be turned ON.

• Some larger drives in older machine may require the use of Disk Management Software for the drive to work. This software is usually provided with the drive (is some cases loaded on the drive). Follow the instructions provided by the manufacturer to extract and use this software.

To complete the Installation:

• Boot the computer from the bootable floppy and run FDISK to set the partition (or partitions).

• Format the drive. If the drive is the only drive, or will be the one that the computer boots from, it must be formatted with the system files.

• Replace the cover.

• The drive is now ready for installation of software.

Motherboards

Installing a new motherboard is one way to do a complete overhaul of a computer. In many cases, it is the most cost-effective method of getting a new computer. This type of upgrade usually works well with IBM “clones.” Many of the larger manufacturers have proprietary motherboards and can only replaced by the same manufacturer make one. Before deciding to undertake this major overhaul, there are several things to consider:

Motherboard

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• Will the motherboard fit into the existing case? Check the size and alignment of mounting holes (plastic stand-offs that keep the circuitry from contacting the case).

• Does the motherboard have the same built-in COM and LPT ports?

• Does the motherboard have a built-in video card?

• Will the existing expansion cards fit the motherboard (correct bus and number of slots)? The expansion slots should go toward the back of the computer where the openings are located.

• Is the power connector on the same side as the power supply? It should be as near to the power supply as possible.

• Will the existing drives (CD, IDE or SCSI) work with the controllers on the motherboard?

• Will the SIMMs on the old motherboard work on the new one?

• Will the upgrade meet your current and future requirements?

Installing a new motherboard is a major task and requires complete disassembly, re-assembly and set-up of the computer and all of its devices. Everything learned in this training will be put into practice during a motherboard replacement. The best advice is to prepare everything ahead of time and to take good notes while disassembling the old motherboard.

Replacing a motherboard:

Replacing a motherboard is probably the most difficult task (from the point of physically replacing parts) that a computer technician will undergo. It is equal to no less than building a computer, as it will, in many cases, require complete disassembly first. Although complex, if you follow this procedure one step at a time you should not encounter any problems.

• Complete an installation checklist and make sure all the necessary parts are available and will fit into the computer.

• Remove the old components.

• Disconnect all peripherals and place them in a safe place. Disconnect all cables inside the computer. Remove all expansion cards.

• Disconnect wires to the case switches. Be sure to write down where they came from and how they were connected. Follow the computer disassembly steps given earlier.

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Motherboard in Case

• Remove the old motherboard.

• Remove the screws and stand-offs. Be sure to place them in a safe place.

• Check all the settings on the new motherboard.

• Install the new motherboard.

Position the stand-offs and make sure they align with the case and the motherboard. Make sure the motherboard is positioned correctly (expansion slots facing the back of the computer). Carefully tighten the screws. Visually check to be sure that the motherboard does not touch the case.

• Re-connect the case switches. Use the notes taken during disassembly to be sure they are in the right place.

• Install the primary components (hard drive, video, etc.) – follow the computer assembly steps given earlier.

• Test to be sure that the computer boots.

• Install the rest of the components one at a time.

• Complete the final testing and install the case.

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Summary

In this chapter, we discussed the principles of disassembling and reassembling a computer. Most importantly, we looked at methods for upgrading several key elements of a computer. The following summarizes the key points of this chapter:

• Disassembly and re-assembly of a computer is a simple process as long as you are organized and prepared.

• The key to successful upgrading is in having the right tools and being sure to document everything.

• Good documentation (before and after) is a requirement of upgrading.

• Preparation is the key to a successful upgrade or repair. Document the system setup, including hardware and software setup, using a computer configuration sheet before you begin the project.

• Prepare a plan of action before beginning a project and stick to it.

• Make sure you have an adequate toolkit, including a bootable floppy disk and any utilities you may need.

• Always create a complete backup of the system you are going to be working on before you begin.

• Implement safety precautions, including ESD prevention.

• Follow the steps for disassembly and re-assembly.

• Memory upgrades are probably the simplest and most common upgrades performed by a Computer Technician.

• Installing a new CPU is a common way of upgrading older computers. Installing new expansion cards is another common upgrade. Before installing (or purchasing) new parts, make sure the parts will work with the system you are working with.

• Installing a new hard drive is not difficult. However, certain procedures need to be followed in order to insure that it will function properly

• Installing a new motherboard is one way to do a complete overhaul of a computer.

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KEYWORDS Exercise

Define each of the following keywords. Hint: There’s a glossary in the back of this book.

Keyword Definition

Chip Removers

Compressed Air

Curved Hemostats

ESD Tools

Flash Light

Multi-meter

Needle-nose Pliers

Nut Driver Set

Screwdrivers

Torx Driver

Tube for Small Parts

Tweezers

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Review Questions Chapter 9

1. Describe a sample toolkit for the Computer Professional.

2. What is a “Torx” driver used for?

3. What do the utilities “Speedisk” and “Defrag” do? Which works with what operating system?

4. How many bootable floppy disks are needed for a Computer Professional Tool Kit?

5. Can you use a utility program, such as Norton’s Utilities that was designed for Windows 3.x on a computer loaded with Windows 95?

6. You are only going to check the memory chips; do you need to use ESD safety practices?

7. SIMMs are available in two physical configurations. What are they?

8. You have an extra 16 Megs of RAM on a single 30-pin SIMM, and a friend has a computer and needs more memory. Can it be installed on your friend’s computer?

9. What is “parity?” Can parity chips and those that do not have parity be mixed?

10. Can L1 cache memory be upgraded?

11. What component in a computer determines if a computer can be upgraded by replacing an old CPU with a new one?

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12. Your client wants to install a second modem. Should they use an internal modem on an expansion card or an external modem? How would you determine which is going to be best for the job?

13. A friend just got a deal on a new PNP sound card and wants to install it on their 486 SX computer. Will it work?

14. How would you determine whether to install an upgraded CPU or another motherboard?

15. What is the advantage of “Plug and Play?” What computer manufacturer was the first to use Plug and Play?

16. What are the four requirements that must be addressed before installing a new drive in a computer?

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Chapter 10 – Printers

Printers have become so common that they are considered a standard component. Many new computers come bundled with a printer as part of the complete package. The fact is that a printer is the most common add-on or expansion to a computer. Printers come in all sizes, shapes and colors. As with all other devices, each type has its own unique advantages and disadvantages.

Printer Basics

For a long time, the printer has been considered a necessity in the business environment. Just like the processor and disk drives, printers have evolved from simple impact printers to high-power color laser printers. Printers have virtually replaced the typewriter in the office.

When evaluating printers you should consider the following:

Print Resolution – Resolution is measured in DPI (dots per inch). This indicates the number of vertical and horizontal dots that can be printed. The higher the DPI, the smaller the dots and therefore the higher the print quality.

Page Capacity – The number of pages the printer will print per minute. Remember that this is based on simple text and not high-resolution graphics. If the printer is to be used on a network in a large office, you should consider the maximum page number requirements per day. This limit, if exceeded, will affect the printer’s warranty.

Printer Memory – Printing large graphics and multiple colors requires memory. The printer must have enough memory to hold at least one page of data.

Cost of Paper – Will this printer require special paper? Some color printers must have special and expensive paper to produce high-quality images.

Cost of Ink and Consumables – You need to calculate the cost per page for printing, not the cost of a replacement ink or toner cartridge.

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Common Printer Terms

Here are some basic terms used with printer communication.

ASCII ASCII (American Standard Code for Information Interchange) is a standard code representing characters as numbers and is used by most computers and printers.

Embedded Printer Commands

Printer commands written by the user directly into a software file.

FONT Font refers to the various sizes and styles of characters.

Landscape The horizontal orientation of printing on a piece of paper so that the text or image is across the 11 inch width of paper.

LPT The name assigned to the parallel printer ports on a computer.

Offline The state in which a printer will not accept data from the computer. If you have offline printing enabled, jobs are spooled but printing can’t take place until offline printing is enabled.

Online The state in which a printer will accept data from the computer.

PCL Hewlett-Packard’s page description language (Printer Control Language) for printers.

Portrait The vertical orientation of printing on a piece of paper so that the text or image is across the 8.5 inch width of paper.

Postscript A postscript printer is a high-speed commercial printer. They are used for high volume applications and not normally found in the general office environment.

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Resolution Enhancement

An HP technology that improves the 300 dpi print quality standards used in laser printers by smoothing the jagged edges of curves. Also called RET.

Spooling Printing documents are spooled by the printer and then to the printing device.

Test page Printers can print a test page from the properties setting of the printer or the button on the actual printing device.

Printer Technology

Printers can be categorized into one of several basic technologies. Each is defined by the method that is used to imprint the text or graphic on a piece of paper. In this section, we are going to look at five different technologies. Notice that each technology has its own advantages and disadvantages.

Impact Printers

Impact printers derive their name from the fact that they print by physically contacting a ribbon with a small hammer. They work just like typewriters except they print dots that are arranged into images of the letters. Impact printers have the advantage of being inexpensive and printing at relatively high speeds. Impact printers were very popular in the late 80s and early 90s. Some disadvantages of impact printers are lower print quality and they can be very noisy. Impact printers still maintain a loyal market-share and are most commonly used for multi-part forms, invoices and checks because of their tractor-fed system that uses toothed gears to pull the paper forward in the printer.

Impact Printer

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Dot Matrix Printers

The most popular Impact Printer is the Dot Matrix printer. Dot Matrix printers form characters as raster images by pressing pins onto an inked ribbon. Dot matrix printers use an array of round-headed pins (i.e. 9 or the more common 24 pins) to press an ink ribbon against the paper. The higher the number of pins, the higher the print quality. The print head in a dot matrix printer is arranged in a rectangular grid or matrix of print wires that are controlled by electromagnets. Dots are created when power is applied to selected electromagnets, which force the desired print wires away from a magnet in the print head. The wires strike an inked ribbon, which strikes the paper. Each character produced by the print head is composed of several rows and columns of dots called “pixels”. By striking the individual dots, a character is formed. The continuous form paper is fed using a tractor feed.

Pixel

Note: The speed of a dot matrix printer is measured in cps (characters per second) whereas the speed of a laser printer is measured in ppm (pages per minute).

Maintaining a dot matrix printer is very simple:

• Change the ribbon.

• Keep it clean.

• Clean the print head.

Troubleshooting of a dot matrix printer usually requires a reference manual. No single guide will help because there are so many printers on the market. If no guide is available, check for instructions on the printer itself. Usually a thorough inspection will allow a technician to detect the problem.

Typical Troubleshooting Guide for a Dot - Matrix Printer

Symptom Possible Cause

Cannot change print mode from computer

Check dip switch settings

Cannot print ASCII characters with code above 127

Check dip switch settings

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Symptom Possible Cause

Continuous Paper/Error indicator flashing

OVERLOAD condition

Head moves but does not print Ribbon not installed properly

Only half of the characters are printing

Defective print heads

Paper bunches up around platen No reverse tension on paper

Paper slips around platen Adjust paper feed selector for size and type of paper

Power is on but not printing Printer is not ON LINE

Printer is out of paper

Print is faint or uneven Replace the ribbon

Printer Dead No AC Power

Fuse Blown

Printer won’t go ON LINE Out of paper

Printout double-spaced or no spacing

Check set-up settings

Daisy Wheel Printers

The other type of impact printer is a Daisy Wheel printer. A Daisy Wheel printer prints characters one at a time using a circular printer element that produces a letter quality output. Each printer element contains one font, which means every time you wanted to change fonts (i.e. from courier to roman) you would have to manually change the element. There are still a few of these printers in existence, however, since the late 80s, they have become almost extinct.

Thermal Printers

A Thermal Printer is a printer that prints by heating spots on the paper with an array of tiny, fast-acting heating elements. Their advantage is they are very inexpensive. Their disadvantage is they require special paper that may discolor with age. An example of a Thermal Printer would be an early fax machine. These types of printer also can be used to print labels and barcodes.

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Thermal Wax Transfer Printer

A Thermal Wax Transfer Printer uses heat to bond a wax-like pigment to paper. Thermal wax transfer printers usually have a standard resolution of 300 dpi, however, the resolution looks coarser due to the fact the colors bleed together as they overprint and form super pixels about five dots across. Because the dots look coarser, the color saturation can be superior to a color laser or color inkjet printer. The technique used by this type of printer is called dithering. Dithering is a process that will simulate gray tones by using different patterns of black and white pixels.

Both the paper and ribbon are passed over the printhead, as shown in the diagram below. The printhead contains hundreds upon hundreds of heating elements that heat the ribbon. The ink dots are melted down and then applied to the paper. Since the ink is wax-like in substance, it sticks to just about any media. This process is similar to the process used in dye sublimation, but photos made with this type of printer don’t look quite as good. Thermal wax transfer printers are faster and less expensive than dye sublimation printers.

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Dye Sublimation Printers

These printers use a ribbon comprised of plastic film that contains layers of cyan, magenta, and yellow. Heating elements move across the ribbon, causing the ink to vaporize and diffuse onto the surface of the coated paper. Since the heating elements are capable of very specific temperatures, color densities are easily controlled.

This process is achieved in three passes, layering the colors on top of one another. A clear coating is used to finish the process to protect against ultraviolet light. Unlike thermal wax transfer printers, dithering is not used. The resolution dye sublimation printers print at is 300 by 300 dpi with a printing time of around 2 to 3 minutes.

Ink Jet Printers

Ink jet printers also called Bubble-Jet printers have replaced the dot matrix printer at the low-end of the market. Many computer manufacturers and large computer stores offer ink jet printers as part of their “package deals.” Ink jet printers heat and spray ink onto the paper in order to form images. The nozzle gate is closed during periods of inactivity. They produce good quality printing and are relatively fast while requiring little maintenance beyond replacing the cartridge. What makes them so attractive is their ability to easily produce color as well as standard black and white printing.

High quality color ink jet printers are available. However, high quality color printing does come at a cost. It requires a good printer and special paper that will prevent “wicking” of the ink causing a fuzzy appearance.

The cost of printing as well as the cost of the printer should be considered when purchasing a printer. It may be cost effective to have more than one kind of printer in an office. Many offices have a heavy-duty high-speed laser black-and-white printer for text printing, a dot-matrix printer for forms and labels, and a color ink-jet for graphics. It is also common to find several printers available on the local office network.

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Typical Troubleshooting Guide for an Ink-Jet Printer

Symptom Possible Cause

Any printer error Run printer’s self test

Power is on but no printing Printer is not ON LINE

Printer is out of paper

Printer won’t go ON LINE after replacing ink cartridge

Cartridge is installed incorrectly

Printer is plugged in, all lights are off, and the printer appears to be dead.

Check the power supply’s fuse and replace with the same type and rating if necessary. Before replacing fuse, check the drive mechanisms and motors for signs of binding. They may need to be replaced before replacing the new fuse.

Print head not printing Check the ink supply and replace the ink cartridge as necessary.

Run the alignment program.

Paper tray is having difficulty Malfunctioning pickup rollers.

Paper will not advance Check the control panel to confirm that the printer is on-line. If the printer is on-line then you will need to inspect the paper handling motor and gear train. You do this by setting the printer off-line and pressing down the form-feed button.

Laser Printers

Laser printers fall within a larger group called Electrostatic printers (EP). They get their names from the fact that they use electro-static charges to move the ink (toner) from a bin to the image on the paper. Standard copy machines also belong to this class of printers. Laser printers utilize two technologies. The first is based on the photoconductive characteristics of some organic compounds. These compounds are light sensitive and when exposed to light, their ability to conduct electricity will change. The second technology, not surprisingly, is lasers. The laser provides the source of light to change the conductivity of the organic particles. One of the primary differences between an impact or ink-jet printer and the laser printer is that laser printers print one page at a time while the others print one line or character at a time.

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Initially, laser printers were considered a luxury item and were expensive. Because laser printers are now very affordable, they have become one of the most popular printers for home use and a must for most office environments. They are known for producing high quality and high-speed printing. Laser printers are a big part of the A+ exam so we are going to look at the various sub-systems that make up a laser printer and how they work together to produce an image.

Note: some laser printers have a duplexer that allows you to print on both sides of the paper.

Laser Printer Sub-System – Toner Cartridge

The toner cartridge is the main replaceable component of a laser printer. Its primary function is to provide toner or the carbon particles for printing the image. However, it also contains several of the key components of the process. These are replaced every time that the toner cartridge is replaced (one of the reasons for the high cost). The advantage of this system is that in the end you will have fewer maintenance problems. Let’s look at these components.

Photosensitive Drum

The photosensitive drum is the key component of the printer that forms the image. An aluminum cylinder is coated with a special photosensitive material that can hold an electrical charge when not exposed to light. This material is made up of individual particles so that if one is charged the adjacent will not necessarily be charged. When light hits one of the sensitive particles, any electrical charge it may have is drained out through the grounded cylinder.

Clean or replace this component for proper maintenance according to manufacturer’s instructions.

The Photosensitive Drum

Primary Corona

The purpose of the primary corona is to evenly charge all the photosensitive particles on the surface of the drum. A wire that is located close to the photosensitive drum (it never touches the drum) generates the primary. A very high voltage is applied to the corona wire, which internally generates an electrical field (or corona) around the wire. To control the charge that is applied to the drum, a primary grid is inserted between the corona wire and the drum. After passing the primary corona, the drum will have an even charge between - 600V and -1000V.

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Toner

The toner is the consumable part of the printing process. It is a fine powder made up of a carbon substance mixed with polyester resins (plastic particles) and iron particles (similar to what is used in a photocopy machine). This strange mix makes for a unique particle that can be electrically charged and attracted to a photosensitive drum, then deposited on paper and melted so that it becomes a permanent image. The small size of these particles makes for very high-resolution images. (No small task for a piece of carbon.)

Developer roller

An additional roller is placed between the storage tank for the toner particles and the photosensitive drum. The function of this roller is to uniformly transfer toner particles to the photosensitive drum.

Cleaner blade

The cleaning blade is used to scrape any excess toner (not transferred to the paper) off the roller before it goes to the corona to be charged.

Laser Printer Sub-System – Laser Scanning Assembly

The laser is a high intensity light source (like all other lasers). It is used to write the image onto the drum. As it scans the rotating drum, it removes the charge on any particles that it hits thus leaving an electronic image.

Laser Printer Sub-System – Power Supply

Laser printers will use two power supplies. While they may be packaged in the same box, they have two different missions. Both convert the incoming source power to the necessary DC requirements. Like the power supply in a computer, printer power supplies are a non-serviceable part.

High-Voltage Power Supply (HVPS)

The laser process needs high voltages to work. The HVPS is responsible for creating a steady supply of high voltages. The corona wire and the transfer corona wire use these high voltages.

DC Power Supply (DCPS)

The DC power supply is similar to the one used on a computer. It creates both 5 and 24-volt sources. Printers need 24 volts, instead of the 12 volts used in computers, because the drive mechanisms use larger motors and therefore require more power.

Laser Printer Sub-System – Paper Transport Assembly

This sub-system is the most mechanical part of the printer. It will vary from manufacturer to manufacturer, depending on the complexity of the printer. We all know

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how paper can jam in a printer. The better this sub-system is designed, the better the printer. Keep in mind that in this one area, low-cost printers are often under-engineered. There are many rollers in a printer, but three of them are special. The feeder roller, the registration roller, and the fuser roller are responsible for special tasks. The feeder roller and the registration rollers require accuracy and are driven by stepper motors. Remember those stepper motors used in early hard drives? These are the same things, only bigger. The feeder roller (also called the pick-up roller) is responsible for picking up one piece of paper at the precise time and delivering it to the registration rollers. The registration rollers are responsible for making sure that the paper contacts the photosensitive drum square and at the right time so that the image will appear at the correct location on the page. The fuser roller is responsible for fusing the toner particles to the paper. These are actually two rollers that are in contact with each other. The fuser roller is heated, which melts the particles. The other is a pressure roller that bonds the melted particles to the paper.

Laser Printer Sub-System – Transfer Corona Assembly

The transfer corona works similar to the primary corona. It is a wire that when applied with a high voltage creates an electrical field. The difference between the primary corona and the transfer corona is the charge. The primary corona is negative and the transfer corona is positive. Its purpose is to charge the paper and attract the particles off the photosensitive drum. In order to prevent the paper from wrapping around the drum, and make it more user friendly when leaving the printer, a static charge eliminator removes the charge from the paper after the particles have been transferred.

Laser Printer Sub-System – Printer Controller Assembly

The controller assembly is the electronic circuitry that runs the entire operation. It receives a signal from the computer or network print server that a page needs to be printed, collects the data into its memory, activates all the components of the printer and prints the page.

The Laser Printing Process

Knowledge of the printing process for the laser printing system is an essential part of the A+ exam. This is the six-step process of laser printing: While these are explained in six discrete steps, keep in mind that this is a continuous process and no one step is actually first or last. Refer to the following drawing as you go through each step. During the discussion, we will be talking about positive and negative charges. You will need to keep in mind that positive or negative is actually a relative term. For example, a 100-volt positive charge is negative relative to a 200-volt charge. Also, do not confuse the term positive image with the term positive charge. A charge is a measurement of electricity. In imaging, a positive image represents the actual image where a negative image represents just the opposite. Just like a photograph and its negative. The following is a graphical look at the laser printing process:

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Laser print process

Condition the Drum

This step sets the stage for the imaging process. Its purpose is to prepare the drum (actually the photosensitive particles on the drum) to receive the new images. To do this, all the particles must have the same charge. As the drum rotates past the corona wire, the particles are charged equally to a voltage between -600V and -1000V.

Write the Image

With all the particles at the same charge, we need to discharge some of them to create an image on the drum. This is where the laser comes in. As the drum turns, the laser writes a positive image on the surface of the drum. A positive image is equal to the image that will be printed. Remember, do not confuse the positive image with the positive charge - they are two different things. Every particle on the drum that is hit by the laser releases most of its negative charge into the drum. The particles that represent the image are now at about –100 volts. This makes them positive when compared to their neighbors that were not hit by the laser (-100 is more positive than -600).

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Transfer Toner

Now we must transfer the toner from its container to the photosensitive drum. This is actually a two-step process. First, the toner is attracted to the developer roller. This is done by applying a – 600 volt charge to the roller. The toner particles are attracted to the roller and then a doctor blade scrapes off excess particles leaving a thin smooth coating on the surface of the roller. Now the toners particles have the same charge as the particles on the photosensitive drum that were not exposed to the laser. Now when the two rollers pass in close proximity, the toner particles are negatively charged when compared to the particles on the drum that were exposed to the laser, and therefore are attracted to the drum. Now we have an image made up of toner on the photosensitive drum. Note; this process is also called developing.

Transfer –Image to Paper

The next step is to get the toner off the drum and onto the paper. This too is done with charges. The transfer corona wire is used to place a +600 volt charge on the paper. Now the paper (at +600 volts) is more positive than the toner on the drum, so as the paper contacts (very lightly) the drum, the toner transfers to the paper. Now there is a small problem. The paper has a +600 volt charge and we need to get rid of it for our own safety. To do this, the paper passes over a static eliminator. This will ground the paper and eliminate the charge. Hint – if you are getting a static discharge from the paper when it leaves the printer (or photocopies), the static eliminator is not properly grounded.

Fuse the Image

The final step in creating the image is to fix the image to the paper. After the image is transferred to the paper, it is only particles of toner resting on the surface. To make a permanent bond, the paper with the toner is passed through the fusing rollers. Here, the hot roller melts the toner particles and the pressure rollers bond them to the paper.

Clean the Drum

Even though we have an image, we are not done yet. We must clean up after ourselves. If the drum is not clean before the printing of each page, printing defects occur (random black spots and streaks). In addition, if you don’t clean the drum well enough, you will see ghost images from the previous page. Cleaning is accomplished with a rubber blade that scrapes the excess toner into a holding bin. If cleaning is not done properly, the drum may be damaged. Damage to the drum will cause a permanent mark to be printed on every page printed after the damage occurs. After physically cleaning (removing excess toner), one or more erase lamps are used to discharge surface particles of the drum to ground.

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When Laser Printers don’t work:

Laser printers are known to be very reliable and cause few problems. Problems may arise however, from either hardware or improper printing techniques. The best source for troubleshooting a printer is the documentation provided by the manufacturer. However, here are a few generic problems that may be encountered with laser printing.

Generic Laser Printer Problems

Problem Cause

“MEM OVERFLOW” Not enough RAM – reduce resolution or RET.

After clearing a paper jam from the tray in a laser printer, the printer still indicates a paper jam.

You need to open and close the top cover to reset printer.

Back of the page comes out dirty

The fuser is contaminated with toner.

Creased Pages Wrong paper thickness or transport roller failure.

Dark Ghosting Damaged drum.

Ghost images appearing at regular intervals on the printed page.

Drum not fully discharged.

Previous images used too much toner – reduce dpi – check toner level.

Hardware Run the self-test to check for connectivity and configuration problems.

Incomplete Characters Adjust the print density.

Light Ghosting Excessive toner.

Light Printing (column) Low toner.

High humidity.

Faulty transfer corona.

Marks on every page. Damaged drum.

Mass of melted plastic. Wrong transparency material.

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Problem Cause

Multiple pages are pulled Humidity is too high.

Wrong paper type.

Worn separation pad.

Page smears Paper could be the wrong type or damp

Page is completely black. Failure of the primary corona.

Paper keeps jamming. Check the pickup area, turning area and registration area.

Printer kicks out printer code

Get correct drivers

Check cabling

Random black spots or streaks.

Drum is not clean.

Warped, overprinted, or poorly formed characters.

Problem either with the paper (or other media) or the hardware.

Wavy image on the page Replace the defective toner cartridge

Solid Ink Printers

These printers are a type of laser printer that uses a wax-like solid ink that is melted into a liquid form before it is applied to the page. The liquid ink is applied to the drum with jets, and from the drum to the paper. This helps to better control how the color looks and is applied.

The speed and the color quality of a solid ink printer generally exceeds that of a laser printer. It prints in one pass instead of four passes.

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Solid Ink Printhead

Before the printhead jets the ink from the nozzles, the wax-like substance is melted to a liquid state and it enters the printhead. The ink is placed on the paper using the piezoelectric drop on demand method. This method of ink deployment drops ink only onto the areas where the image is desired, thus restricting ink consumption.

Solid Ink Printhead

Electromagnetic Transfer Method

Replacing the Ink Blocks

The ink blocks are generally shaped differently to prevent incorrect placement.

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Printer Image Concepts

Printing is a complicated process that requires incorporating many different techniques. This section is going to look at several of these concepts.

Character vs. Raster

The difference between character printing and raster printing is the difference between printing text and printing a picture. When printing characters, such as when using a dot matrix printer, the computer sends the printer information one character at a time. Each character will equal one byte of data. A blank line is equivalent to one character therefore only one byte of data. Printing text is fast only because the amount of data is small. Most printer manufacturers today will rate the print speed (pages per minute) based on text-only printing. An average page of text requires about 23KB of data or memory.

Printing a raster image is like printing a picture. The image or the entire piece of paper is composed of a grid of dots. Each dot is one bit of data (eight dots is one byte). Depending on whether or not the bit is on or off, a dot will be printed. The computer sends data to the printer in a stream of bits and the printer reproduces the dot pattern or raster image on the paper. A typical raster image of one piece of paper is about 1 megabyte of data or memory. The resolution determines the actual size of the image data.

Resolution

In the chapter on displays, we discuss monitors and resolution. When it comes to printing, resolution is similar, but not the same. In a display, we look at pixels and resolution as a function of how many pixels we can get on the screen. In printing, we are more precise and can actually measure the resolution. Resolution is defined as dpi (dots per inch). Pixels in monitors are rectangular and can vary in size. With printing, we are concerned with the number of dots per inch that will be the same both horizontally and vertically. So a printing resolution of 300 dpi is 300 dots horizontally and 300 dots vertically. Some printers may boast resolutions such as 600x1200, but these are the exceptions and found only in commercial-grade printers. Printing resolutions will run from about 100 to 1200, with 300 being considered good quality and 150 dpi being considered draft quality. Printing resolutions are superior to monitor resolutions that run about 50 to 80 dpi.

Higher resolutions produce higher quality images, but at the expense of more memory and toner. Keep in mind that each dot, whether black or white, requires one bit of memory. Therefore, a one page 300-dpi image will require about 1 megabyte of printer memory and a 600-dpi image will require about 4 megabytes of memory. If you have a printer with 1 megabyte of memory, you may not be able to print a full-page graphic at 300 dpi. Hint: printing draft and text only documents at a lower resolution can extend the life of a toner cartridge by approximately 50%. This can significantly reduce the cost of operation.

Note: Adding color or gray scale images will increase the image size by up to three times.

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High Quality Printing

Printing high quality images can be tricky. Most printing, whether dot matrix or laser, will leave jagged edges on an image. This is simply a matter of the size of the dots and the grid pattern. The easiest method of producing high quality images is to increase the resolution. The smaller the dot, the smaller the jagged edge. This method does come at the price of memory.

Fortunately, modern technology has provided a few ways to resolve this issue without using too much memory. The first is called RET or resolution enhancement technology. This method uses a combination of large dots (primary resolutions) and smaller dots to fill in the jagged edges.

RET

The second method is called interpolation. With this method, a printer will print at a higher resolution than the image that is sent to it. For example, you may send a 300 dpi image to the printer, but it interpolated the image to 600 dpi. While this is not as good as sending a 600 dpi image, it does use less memory and speeds up the process.

Computer to Printer Communication

For a long time, the language of printers was ASCII. The computer sent a stream of bytes to the printer in ASCII code that was in turn converted to text. This format of printing uses escape code sequences to control the process. This works great for text-based printing. However, today’s printers are image-based and require special languages to send the data. These special languages are called Page Description Languages (PDL). They derive their name from the fact that they send an entire page of information at one time. Let’s look at two of the more popular printer languages:

PCL – Printer Control Language

PCL is the standard PDL used today. Hewlett-Packard developed it in the early 1980s. Many printer manufacturers provide some form of emulation for their printers. PCL is comprised of four sets of commands.

Control Codes – the standard ACSII codes from the old days.

PCL commands – these provide the basic page formatting factions.

HP-GL/2 – the commands necessary for printing vector graphics.

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PJL (printer job language) command – these commands enable the printer to communicate with the computer to control printer jobs.

The latest version is PCL 6 released in April 1996. The key to using these languages is to make sure that the printer and the print driver support the same language.

PostScript

PostScript is the language of the commercial printers. If you are serious about printing and intend to start publishing, you will need to use a PostScript printer. This is the industry standard for desktop publishing and graphics. PostScript printing was developed by Adobe and introduced in the Apple LaserWriter printer in 1985.

Multifunction Printers These printers are common nowadays and help to meet office needs for faxing, scanning, printing, and copying. These printers also help to save desk space.

Multifunction Printer

Plotters

Plotters can be used with CAD applications (such as Autocad) for designs such as blueprints. Architectural and engineering firms use plotters to aid them in their design efforts.

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Printer Accessories There are a great deal of printing accessories available for printers today. The following accessories aren’t necessarily inclusive, since new accessories are being designed all the time. The following accessories are representative of the majority of printer accessories.

Internal Print Servers

These expansion cards allow printing devices to be managed without increasing the load on the computer. They function in much the same way as an external print server.

Post Script Upgrade Software

You can also purchase postscript upgrades for your printer to increase its functionality.

Duplexer

This accessory allows for double-sided printing. Higher end printer can have integrated duplexers.

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Paper tray

Paper trays help to expand the amount of paper that you can use before reloading.

Memory

Addition printer memory generally ranges anywhere from 8MB to 128MB. Additional memory allows a printer to print pages faster, with more dots per inch, or with more high-resolution graphics on a page.

Sheet Stacker

Sheet stacker help to automate the stacking of your printed documents as they are printed.

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External Printer Server

External printer servers take the load off the computer by handling the print jobs by itself. Plus, since it is a network device, all users can access it.

Folding Machines

Folding machines automate the folding of documents like brochures and pamphlets.

Printer Hard Drives

Hard drives, when used with printers, allow the printer to upgrade software and handle bigger jobs.

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Staplers

Staplers automate the stapling process for multi-sheet documents.

Network Cards

Network cards allow a printer to have a network identity (through IP addressing).

Automatic Document Feeder

This accessory helps to speed up the number of documents that can be scanned; eliminating the need to hand feed each one. These are used on multifunction printers.

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Printer Installation

Selecting a printer can be a very complicated task. The computer technician must be able to compare the specifications of the printer to the job requirements and to insure that the printer will be compatible with the computer. Some printers may require a special port or may not be compatible with other devices connected to the computer. Fortunately, most of today’s printers are Windows 9x compatible and will install easily using Plug-N-Play technology. Most printers today use parallel ports (also referred to as a Centronics connector). The Centronics standard was introduced on the original personal computer. The common parallel port on a computer uses a 25-pin female connector. You would simply connect the Centronics-compatible end of the printer cable to the printer and install the other end to the appropriate LPT port and you should be off and running.

For the few printers that aren’t Windows 9x compatible, installation can be slightly difficult. For example, you may have to load a device driver to configure the software for the correct printer. If you are setting up serial printers, the serial port may need to be configured for parity type, speed, and protocol. Installation may vary depending upon which type of printer you have.

The key to installing a printer is to be sure that you have the latest driver that matches both your printer and your operating system. For example, if you are installing a printer on a Windows NT machine, it will most likely need special drivers. NT drivers are not always provided with the software that comes with a printer so you will have to find one. The best place to look is the manufacturers Web site. Most printer manufacturers will provide a site for downloading the latest drivers. If the manufacturer does not provide a driver, try www.drivers.com. They have drivers for almost every device you can imagine. I have found drivers that the manufacturer could not provide. Moreover, they worked.

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Summary

Understanding peripheral devices and printers is an important part of A+ certification. The following is a summary of the key points of this chapter.

• There are three main types of printers (Impact, Ink Jet and Laser).

• The key components of a laser printer are: Power Supply, Photosensitive Drum, Primary Corona, Laser, Transfer Corona, Transport System and Controller.

• The six steps of laser printing: 1. Charge the drum. 2. Write the image. 3. Transfer toner to drum. 4. Transfer the image to paper. 5. Fuse the image. 6. Clean the drum.

• Resolution enhancement or RET is one method of improving print quality.

• Printer resolutions are different from display resolutions and are measured in dpi (dots per inch).

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KEYWORDS Exercise

Define each of the following keywords. Hint: There’s a glossary in the back of this book.

Keyword Definition

ASCII

Cleaning blade

Daisy Wheel printer

Developer Roller

Dot Matrix printers

Embedded Printer Commands

FONT

Impact printers

Ink jet printers

Landscape

Laser

Laser printers

LPT

Offline

Online

Page Capacity

PCL

Photosensitive drum

Pixel

Portrait

Postscript

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Keyword Definition

Primary corona

Resolution

RET

Spooling

Thermal Printer

Thermal Wax Transfer Printer

Toner

Toner cartridge

Transfer corona

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Review Questions Chapter 10

1. Name three types of printers and their advantages and disadvantages.

2. The dot matrix printer is a/an ________ printer. What is an advantage of this type of printer? A disadvantage?

3. Wicking can be a problem with ink-jet printers. How can it be prevented?

4. What are the six steps of laser printing?

5. What components are usually included in a laser printer’s replaceable toner cartridge? Why?

6. What will cause black spots on paper printed on a laser printer? How can this problem be resolved?

7. Besides the cost of the printer, what other costs should be considered when purchasing a printer?

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Chapter 11 – Monitors

The majority of our discussions about computers have been focused on what goes on inside the computer. In this chapter, we are going to talk about the most used output device that we use with computers – the monitor.

Displays

A display is a monitor, the primary output device for a computer. Every computer will have some form of display whether the standard video monitor, an LCD (Liquid Crystal Display), or one of the new thin monitors. In this section, we are going to look at three aspects of displays - the displays themselves (monitors), the video cards that drive them, and the memory required to gain the performance we need from them.

Display Technology

Just like computers, monitors developed over time. The early 8088 computers were designed to process data in the form of text. There was little need for color or graphics. Some of these early monitors were considered color because they were black and green or black and amber instead of black and white. These “colors” made it easier on the operator’s eyes. In today’s world with Windows and multimedia, choosing a monitor is not so simple. In this section, we are going to look at the development of monitor technology.

Monitor Technology

The most common of all displays is the video monitor. For most of us, it looks like a television screen. While it operates on the same principles of a television, the specifications are quite different. Since the predominate feature of a standard monitor is the screen itself, let’s start by taking a closer look at the cathode ray tube (CRT) also known as the screen.

CRT

The cathode ray tube is the only vacuum tube still being used in computers and televisions. It consists of a conical shaped tube on which one end has been elongated. On the large flat end of the cone is the screen that we look at. The other end contains the electron guns that create the lighted image on the screen. In the middle are various coils and electronic circuitry that control the formation of the image.

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CRT

Fortunately, as A+ technicians we do not have to know how all this works, but it does help if we have an understanding of the principles of image generation. With this knowledge, we can effectively select the right monitor for the job.

A CRT works like this. An electron gun at the long narrow end is heated and emits a stream of high-speed electrons in the direction of the large end of the tube. When they hit the other end of the tube, they contact a phosphorous material that gets excited and glows forming a dot that we can see from the screen side of the tube. In between the electron gun and the end of the tube are the controlling coils. These coils (called the yoke) generate magnetic fields that can deflect the flow of electrons emitted by the electron guns. By varying the current in these coils, the beam can be directed to any point on the screen. By varying the heat to the electron gun, the intensity of the electron stream can be controlled, thus providing various shades of intensity. Now, putting all this together, and scanning the surface of the screen in a uniform and predictable pattern, while varying the intensity of the beam, can form an image on the screen. This is how a monochrome or black and white monitor works.

A color monitor on the other hand is three times as complex. Instead of one electron gun and beam, it has three. Each beam is aimed at a different dot of phosphorous that will emit red, green or blue colors. By combining these three colors, (and varying the intensity of each beam) almost any color can be generated. Sounds complicated and it is. Fortunately, we do not have to know how it works, just the effects of how it works. We will do this by reviewing some common terms.

Persistence vs. Scanning Frequency

These are two concepts that work against each other and therefore must be balanced. Persistence is the time that a phosphorous dot will continue to glow after it has been excited by an electron beam. Scanning frequency is the amount of time it takes for an electron beam to scan the entire screen and return to a dot. This is also called the refresh rate. The proper balancing of these two functions will eliminate any flicker and ghosting of images. If the persistence is too low compared to the frequency, the dot will not retain enough light and the image will flicker. If the persistence is too high, there will be too much light and a ghost image will appear.

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Sweeping and Refresh Rates

As we said, the electron beam(s) are controlled so that they energize every dot on the screen. This is done through a sweeping action. As we look at the screen from our side, the electron guns are swept from the upper left corner, horizontally across the screen, turned off and moved to the left and down one dot (horizontal retracing), turned on and then swept horizontally again. When the beam gets to the lower right corner, it is turned off and moved back to the starting point (vertical retrace).

CRT Sweeping

The time or frequency for these sweeping actions is called the refresh rate. The measurement of refresh rates is hertz (Hz) or cycles per second. The time to scan one line is called the horizontal refresh rate (HRR). The time to scan an entire screen is called the vertical refresh rate (VRR). The important number to us is the VRR. This is typically about 70 Hz. An abnormally low refresh rate will cause flicker (same as low persistence) that can lead to eyestrain. If the refresh rate is too high, the image can become distorted or ghostly. High refresh rates can also cause damage to the electronic circuitry of the CRT. You might even need to go into safe mode, if you change the refresh rate.

Interlacing

Interlacing is a way of arranging a video display so that the CRT sweeps all the odd-numbered rows then all the even numbered rows (or vice versa). Interlacing is suppose to reduce the flicker on the screen by increasing the refresh rate (scans the screen twice as often). In practice, interlacing reduces flicker only when adjacent rows of colors are similar. Interlacing works well on TVs, but not computer monitors.

Note: Interlacing can lead to eyestrain and headaches.

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Interlacing is a feature of low end, inexpensive monitors. An interlaced monitor may be well suited for stand-alone servers or monitors that run long hours unattended. This may be a good choice when there will be little interaction by an operator (service situations) and cost is a primary factor. Interlacing should be avoided for normal use.

Thin CRTs

A company out of San Jose, California has developed what it believes is the answer in new CRT technology. They call their product the ThinCRT® and they claim that it is the answer to low power, low cost, high-speed displays that marries the best of the LCD flat screen with the color and performance of a color monitor.

This technology uses a cold cathode technique that generates electrons at room temperature. The Thin CRT consists of two pieces of glass that are approximately one millimeter apart. The “faceplate” is coated with conventional color phosphor and the “baseplate” consists of some 2,000 cathodes that are used to generate the colors. The response time is said to be 10 times faster than the LCD and the view angle is superior. It will use a CRT technology on a flat panel monitor that is only a few inches wide.

Though the company was founded in 1991, so far no products have reached the production stage as of yet. They have generated a lot of interest in the industry and have raised millions of dollars for its research. They expect to reach the pilot stage by late 2001 and take over the display market by the end of the decade.

LCD Displays

A common alternative to the standard CRT is LCD or liquid crystal display. While mostly used with laptop computers, they are now more common with desktops. You will find them as the new thin line or flat panel displays. The difference between these and the standard monitor is that instead of exciting phosphorous to emit light, they apply power to crystals. They are powered by low voltage DC from the power supply, much like the other devices in a computer. We will look at these in more detail in the chapter on portable computers.

Gas Plasma Displays

This type of display is an alternative to LCD. It uses a gas-plasma technology to emit the lighted dots. It is not very popular and is limited to monochrome (usually amber) displays.

Image Technology

Getting a high-quality image on the screen is an important element of working with displays. Getting a high-quality image depends on two things, the size of the display and the resolution. The size issue is simple, the bigger the screen, the more you can get on it. Resolution is dependent on the physical characteristics of the monitor. Let’s start by looking at the resolution of displays.

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Resolution is a measurement of the detail that can be shown in images produced by a monitor or printer. It is normally measured in terms of dots per inch. The human eye normally resolves (starts seeing individual dots) about 150 dots per inch at normal reading distance, however, on close examination, we can resolve 2 or 3 times that much.

Display resolution is shown as the number of horizontal pixels by the number of vertical pixels. A pixel gets its name from the picture element and is defined as the smallest unit of a single color. In a monitor, a pixel is rectangular and made of many small dots (all the dots in a pixel are the same color). The total number of pixels on a screen is determined by multiplying the number of horizontal pixels by the number of vertical pixels. This value is represented as total pixels/screen (800 x 600 = 480,000 pixels/screen). Be careful and don’t confuse the term pixels with dots.

Color monitors (virtually all monitors today are color monitors) have three electron guns, which generate red, blue and green phosphorous dots. The numbers used to determine resolution is the number of distinct pixels not the number of dots. The higher the resolution, the fewer the dots used to create one pixel. Conversely, the lower the resolution, the more dots are used to create one pixel. The lower the resolution (more dots per pixel) the less sharp the image.

On a monochrome monitor, the smallest element is the dot. In a color monitor, it takes three dots to make the smallest element. These three dots (Red, Green, and Blue) make up a triad. Dot pitch is a term that is only used on a color monitor and is the distance between two triads. This distance is measured in millimeters. Dot pitch can be measured as the distance between any two-color dots of the same color.

Color Dots on a Monitor

The dot pitch of a monitor will define the limits of resolution. Most monitors are operated at lower resolutions than their maximum. Let’s look at how dot pitch can affect the maximum resolution of a monitor. For comparison purposes, we’ll look at dots per inch.

Dots per Inch to Dot Pitch

1” = 25.4mm

25 4._ _

_mm

Dots per InchPitch mm=

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254._

_ _mm

Pitch mmDots per Inch=

Monitor Pitch and DPI

Pitch (mm)

DPI

.41 62

Color .31 82

Displays .28 91

.26 98

.25 102

.21 120

Monochrome .17 150

Displays .11 231

Dot pitch works in tandem with the maximum number of lines the monitor can support to determine the greatest working resolution of the monitor. The dot pitch can range from as high as .41mm to as low as .11mm on some monochrome monitors. .28mm is the average dot pitch of today's monitors. High-end applications such as graphic arts and engineering will use monitors in the .21mm to .26 range. Very high-resolution applications such as document imaging will use monochrome displays with .11mm or .17mm dot pitch.

Note: When comparing advertised prices make a note of the monitor’s dot pitch in the ad. The lower the price, the higher the dot pitch.

Summary of Resolution:

• A dot is the smallest element of a monochrome monitor screen.

• Triad - a triangle of three dots (one red, one green, one blue) is the smallest element of a color monitor.

• The number of triads ultimately defines a monitor’s maximum resolution.

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• Display resolution – is based on a pixel or picture element. A pixel is a group of dots that display the same color.

• The distance between two dots of the same color is pitch. Pitch is measured in millimeters.

We will discuss video standards in the next section, but for reference, here are some standard monitor resolutions.

Standard Resolutions

Standard Resolution Minimum Monitor Size

VGA – Video Graphic Array 640 x 480 13-inch

SVGA – Super VGA 800 x 600 15-inch

XGA – eXtended Graphic Array

1024 x 768 17-inch

UVGA – Ultra VGA 1280 x 1024 21-inch

The second measurement of image displays is the size of the monitor. Computer displays are measured in diagonal inches across the screen. Just like television screens, the specified size and the actual viewable size are somewhat different. The “size” specification is based on the total area of the phosphorus screen (including the area where the tube wraps around the edges), while the viewable area is based on the size of the image projected (pitch). The viewable size can be calculated as follows:

• Obtain the specifications for maximum resolution (horizontal and vertical).

• Convert the units to inches.

• Apply the Pythagorean Theorem1 (a2 + b2 = c2) to get the diagonal measurement.

1 Pythagorean Theorem - the sum of the squares of the sides of a triangle equal the square of the hypotenuse.

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Pitch DPI Table

Pitch DPI Horizontal Vertical Size

Resolution Inches Resolution Inches Inches

0.25 102 1024 10.04 768 7.53 12.55

0.25 102 1600 15.69 1200 11.76 19.61

0.21 120 2048 17.07 1536 12.80 21.33

Displays and Power

Monitors are the number one consumer of power (more than half) used by a computer (typically 80 - 100 watts). To deal with power management issues, the Video Electronics Standards Association (VESA) has created specifications for Display Power-Management Signaling (DPMS). These standards define the signals that a computer can send to a monitor during idle times. In addition, Microsoft and Intel jointly developed the Advanced Power Management (APM) specification. These specifications define the BIOS level interface between the hardware and the operating system. In order for a computer to provide power management, it must comply with both of these standards. DPMS on the monitor side, and APM on the computer side.

Working together, these two standards provide four levels of operation.

• ON – This is normal operation at 100% power.

• Stand-By – This level reduces the power to a minimal amount while allowing for a quick recovery. Could be considered short-term power savings.

• Suspend – This level reduces the power to a bare minimum. Recovery time will be substantially longer than from stand-by. This should be considered long-term power savings.

• OFF – This level is the ultimate in power savings. Power is removed from the monitor and it will have to be re-started.

If your system is not compliant with these specifications, you will have to resort to manual power management. That is turn off the monitor when you will be away for a long time. This is assuming that you want to leave the computer running, such as overnight.

Resolution divided by DPI (a2 + b2 = c2) From Table

Above

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DPMS can be configured with hardware, software or a combination of both. The method for a particular monitor will depend on several factors, determined by the manufacturers and the operating system on which it will be installed. If you want to change the DPMS setup:

• Check the BIOS and run CMOS setup.

• Check the operating system.

• Use the software provided by the manufacturer.

Note: an energy-star compliant monitor can save power if no activity is detected.

Green Monitor

Green Monitors are not green in color. This term is used to define monitors that are user friendly. Much has been made to the long time exposure of operators to potentially harmful electromagnetic fields. The concern is that VLF (very low frequency) and ELF (extremely low frequency) emissions might affect the body. While the risk of harm is low, many people today spend at least 1/3 of their day looking at monitors.

Green monitors meet current standards for low emissions. These monitors will typically cost up to $100.00 more than a standard monitor. Green monitor or not, here are some guidelines for protection.

• Stay at least 2 feet from the monitor. Emissions drop off substantially with distance.

• Stay in front of the monitor. Emissions are stronger on the sides than from the front.

• If you must be on the side or back, stay at least 3 feet away.

• Use some method of reducing screen glare such as an antiglare panel. They also provide some protection from ELF and VLF.

Display Adjustment

A few common adjustments can be made to increase the viewability of the screen. Normally you will find a control panel on the front of the monitor. You will be able to make the adjustment directly or enter a menu on the screen to lead you through the adjustments. The following is a summary of the most common adjustments and the symbols to designate them.

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Typical Monitor Adjustments

Vertical Height Allows adjustment of the top and bottom of the image. Image height changes.

Vertical Center Allows adjustment of the location of the image relative to the top and bottom.

Pincushion Adjusts the center of the image (vertically) so that it is square.

Horizontal Width Allows adjustment of the left and right sides of the image. Image width changes.

Horizontal Center Allows adjustment of the image to be horizontally centered.

Keystone Allows adjustment of the top and bottom edge widths so that the image is square.

Degaussing Available on newer, larger monitors. Demagnetize the CRT thus preventing an electron beam from bleeding over to an adjacent dot, causing shadowing and or loss of color control.

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When a monitor goes bad

When it comes to monitors, for a computer technician they should be considered just like power supplies. There are no internal serviceable parts.

CAUTION - VIDEO MONITORS HAVE INHERENT DANGERS FROM THE HIGH FREQUENCY/HIGH VOLTAGE POWER REQUIRED TO OPERATE (UP TO 50,000 VOLTS). SERVICING AND ADJUSTMENT OF THE INTERNAL COMPONENTS SHOULD BE LEFT TO A MONITOR SPECIALIST!

There are only two kinds of display problems. Either it doesn’t work or the image is bad. Let’s first look at the monitor that doesn’t work.

You know when a monitor is not working, because the computer is ON and the screen is blank. When this happens, there are only three places to check.

Power – Is it turned ON? Is it plugged in? Is there power to the power strip or outlet? Sounds simple, but an unplugged monitor frequently is the problem. Most monitors will have a status indicator light to show that it has power. If all is well, the light will be green and if there is power, but no data signal the light will be yellow.

Data Cable – Is the data cable connected securely and to the right connector? If you have a yellow status indicator light, this connection is most likely the problem.

Brightness and Contrast – These controls are used to adjust the intensity of the screen. If set too far one way or the other, the screen will be black. If the status indicator is green, you have power and data signals, so be sure to check brightness and contrast before you panic.

If none of these work, the problem is the video card or the monitor. You can connect a known good monitor to this computer or connect this monitor to a known good computer to isolate the problem.

When the picture is bad, you have a few possible solutions. Some adjustments can be made from outside of the monitor. There are also some inside adjustments, but they are best left to a specialist. The external ones include brightness and contrast. Check the documentation that comes with the monitor to determine the adjustment limits for the monitor. Check for bent pins if a predominant color is the issue.

The cable connection is a common cause of poor picture. An improper connection can cause poor edges and missing colors.

Monitors operate by using magnetic fields to control the movement of the electrons on the screen. Since they rely on magnetic fields, they are also subject to interference from outside magnetic fields. Most have automatic internal circuitry to correct these problems. These are called degaussing coils. If you notice swirls or fuzziness, the monitor might need degaussing. If you push the degaussing button, the image on the screen will shake rattle and roll for a few seconds and then stabilize.

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The following are a few tips to keep in mind for maintaining a quality image on a monitor:

• Clean the screen on a regular basis.

• Use quality cables and insure that the connections are tight.

• Enable any power management features.

• Keep the ventilation slots free from obstruction. The monitor produces a lot of heat and needs to have adequate cooling.

• Use only the refresh rate recommended by the monitor manufacturer.

• Keep magnetic objects away from the monitor screen.

Video Display Adapters

The second key component of a display system is the video adapter card. This device interfaces between the monitor and the CPU. Remember that with any system, it is only as good as the weakest part. Therefore, you must be sure to match the video card to the monitor. As with all other components found in computers, the video adapters have changed with time, beginning with basic monochrome cards for black and white displays and continuing to today’s high-resolution cards with millions of colors. The following identifies the basic adapter card types as they evolved. Nowadays, many have their own BIOS.

Monochrome Display Adapter (MDA): MDA was the first available display type and was introduced in 1981. These were text only and provided a resolution of 720x350 pixels. An MDA is perfect for use with DOS-based text only programs. MDA did not support any graphics beyond horizontal and vertical lines. The MDA is connected with a 9-pin male connector.

Color Graphics Adapter (CGA): This was the first card to support color and graphics. These cards will operate in two modes. The standard mode provides for 16 colors, but no graphics. When in graphic mode, you can obtain a medium resolution (320x200) with four colors or high resolution (640x200) with two colors. CGA also uses a 9-pin connector.

Enhanced Graphics Adapter (EGA): This was the next generation of video produced by IBM. With this card, color began to be more viable as it offered several modes of color and resolution. As with its predecessors, color and resolution is still a trade-off. With 16 colors, you could achieve 320x200 or 640x200 resolutions. In monochrome mode, you could achieve 640x350 resolutions. With this card, the issues of memory and video began to be recognized. It utilized all the memory reserved for video by the BIOS and allowed for the addition of a memory graphics expansion card. Through various combinations, you could get up to 256K of video memory.

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Professional Graphics Adapter (PGA): This adapter card was designed specifically for the professional market (hence its name). With its introductory price tag of over $4,000, you can see why it did not become very popular except in the professional engineering and graphic arenas. However, with it came many innovations for manipulating graphics that are now considered standard.

MultiColor Graphic Array (MCGA): IBM integrated this special adapter into the PS/2 computer line. One of its unique attributes was that it could display up to 64 shades of gray. With this, monochrome monitors could display (convert) color images.

Video Graphics Array (VGA): VGA introduced a new way of operating video. Previously all video cards were digital. VGA introduced an analog system. This may seem strange since today the emphasis is to convert everything from analog to digital. By using an analog signal, colors can be produced at 64 distinct levels. Since there are three primary colors that can be mixed, this gives us a maximum of 643 or 262,144 colors. Quite a jump from 16. In reality, VGA will display up to 256 colors depending on resolution and whether or not it is used in text or graphic mode. VGA introduced what is now the standard video connection, the 15-pin, three-row, female DB type connector. On newer computers, the connection is color coded as blue. VGA is typically the display resolution and color depth referred to on many software packages as a minimum display requirement.

Super Video Graphics Array (SVGA): SVGA is standard on computer monitors. Video Electronic Standards Association (VESA) has established standards for SVGA. These standards cover every resolution and color depth up to 1280x1024 with 16,777,216 colors. When a specification requires “standard SVGA,” they mean 800x600 with 256 colors.

Displays and Memory

Video cards have given us a lot of flexibility for selecting resolution and monitor sizes, however, without sufficient memory; the actual output will be limited. The original BIOS memory map allowed for only 64K of memory. Today’s video cards come with lots of memory and room to add more. You will find anywhere from 256K to 8MB on these high-performance cards. The big question is how to calculate the correct amount of memory for the job.

To calculate memory requirements, you will need to know the resolution at which the monitor will be operating (not the maximum) and the color depth. Resolution is the number of horizontal pixels times the number of vertical lines (or pixels).

Color depth is the number of memory bits used to create the color for one pixel of resolution. These are binary numbers, so if you use 4-bits to control color, the number of colors will be 24 or 16 colors. If you use 8-bits, the number of colors will be 28 or 256. A 24-bit color card is capable of 16,777,216 colors.

Note: Sometimes you will see color depth expressed in terms of bytes instead of bits so you will have to make the conversion. A color depth of two is 2 bytes x 8 bits/byte or 16.

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Color Depth vs. Number of Colors

Color Depth bit/byte Number of Colors

4/.5 16

8/1 256

16/2 65,536

24/3 16,777,216

To determine the minimum amount of video required, all you need to do is multiply the resolution (horizontal x vertical) times the color depth in bits.

Memory Requirement = Horizontal Pixels x Vertical Pixels x Color Depth

EXAMPLE: You have a client that wants to run a resolution of 1024x768 and 16-bit color. What is the minimum video requirement?

Answer: 1024x768x16 = 12,582,912 bits (we need to know how many megabytes are required because that is how we purchase memory).

So: 12,582,912 /8 = 1,572,864 bytes (we are still not there) Remember:

Divide by 1,048,576 to convert bytes into MB of memory

1,572,864/1,048,576 = 1.5 MB

The next question is what kind of memory can we use for video. The obvious would be our old favorite DRAM. DRAM was used initially and is good inexpensive memory, but for video, we need something much faster. Since we don’t need very much (by computer standards) we can afford to invest in memory designed for video. Let’s look at some options.

VRAM

VRAM is designed specifically for use on video cards. It is dual-ported memory. This means that two different processors can access it at the same time. For example, the CPU and the video processor on the card can use it at the same time. This significantly increases the speed of video operations. Just like cache memory, VRAM is expensive so its use is limited to necessity. VRAM is typically used on high-end systems that require lots of speed.

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WRAM

WRAM (Windows Accelerator Card RAM) is another dual-port memory. It is similar to VRAM, but has two advantages.

• Faster - 50% performance increase

• Less expensive - by 20%

MDRAM

Multibank DRAM (MDRAM) is a newcomer to the video memory arena. It is marketed specifically for graphic and video applications. In this case, video means video production not a computer video.

SGRAM

SGRAM or Synchronous Graphics RAM is another high-end memory designed specifically for high-speed graphics solutions. It is called synchronous because it can synchronize its speed with the speed of the motherboard.

EDO

EDO – Extended Data Out RAM (same as used on main memory) has found some applications for video. It is common because of its greater performance than standard DRAM and yet still low in cost as compared to other options.

Un-accelerated vs. Accelerated Video Cards

Today, most video cards incorporate some form of acceleration. What this means is simply that the video card performs the video calculations that were formerly done by the processor. (Un-accelerated cards merely translated what the processor produced into a form that the monitor could display.) This allows the processor to get back to work on something else. This in effect, makes the video card a co-processor that works with the main processor.

Accelerated Graphics Port (AGP)

The AGP port allows the video processor to access system memory to perform video calculations, but keeps dedicated video memory for the frame buffer. More flexible memory use without the sacrifice in performance is achieved with this system. It has become a standard in modern PCs, and with the trend continuing towards 3D animation and full-motion video playback; we can expect future improvements in this technology or others like it.

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Adapter Troubleshooting and Maintenance

There is not much you can do to troubleshoot adapter cards. Either they work or they don’t work. The best technique is to replace it with a known good one. The second best thing is to contact the manufacturer. If you don’t have any documentation, be sure to search the Internet.

Maintaining a video card is easy. Always make sure that you have the latest drives. If you upgrade an operating system, be sure to upgrade the video driver as well.

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Summary

Understanding displays is an important part of A+ certification. The following is a summary of the key points of this chapter.

• The CRT (Cathode Ray Tube) is the main component of a monitor. The slender end of the cylinder contains an electron gun and the bigger end is the display screen.

• Display resolution is a measurement of the detail that can be shown in images produced by the monitor. It is measured in terms of pixels.

• Monitors are the number one consumers of power in a computer system.

• Monitors can store up to 50,000 volts. Opening a monitor is dangerous and should never be worked on without first discharging!

• The video card is the interface between the expansion bus and the monitor.

• The PGA, VGA and SVGA monitors use a 15-pin, three-row, female DB connector.

• Video memory requirements are calculated by multiplying horizontal pixels by vertical pixels by color depth. Remember to convert bits into Megabytes.

• There are two types of DRAM used for video memory: VRAM and WRAM.

• Video cards have grown from simple monochrome to more than 64,000 colors.

• VGA is considered the minimum standard for applications today.

• SVGA is found on most computers sold today.

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KEYWORDS Exercise

Define each of the following keywords. Hint: There’s a glossary in the back of this book.

Keyword Definition

APM

CGA

CRT

Degaussing

DPMS

Dot

Dot pitch

EDO

EGA

Gas Plasma Display

Green monitors

Interlacing

LCD

MDRAM

MDA

MCGA

Persistence

PGA

Refresh Rate

Resolution

SGRAM

SVGA

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Keyword Definition

Thin CRT

Triad

VGA

VRAM

WRAM

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Review Questions Chapter 11

1. Describe the three elements that make up one dot of color.

2. What is the advantage of interlacing? Is it worth it?

3. Should a monitor be turned on and off, or left on all day?

4. What is the “standard” type of video card used with today’s computers?

5. What is the formula for calculating the required memory for a monitor/video card combination?

6. What are HRR and VRR?

7. Why is it dangerous to open the monitor’s cover?

8. What are the four primary sources of video problems?

9. Explain the differences between VRAM and WRAM.

10. What is a raster line?

11. What type of connector is used for an SVGA monitor?

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Chapter 12 – Modems

Today, the technological world moves by electronic communication. Advancements in both hardware and software have made the communications industry one of the fastest growing industries in the world. In today’s fast track of satellites, digital communication (fiber optics) and the Internet, a computer is not considered complete unless it has a modem. The modem connects us through our computers to the world.

Modem Basics

A modem is a peripheral device that enables computers to communicate with each other over conventional telephone lines, ISDN cable lines, and wireless. The word modem comes from combining the words MOdulator and DEModulator. In the radio business, to modulate a signal is to change the frequency (FM) or amplitude (AM) of a carrier (fixed signal) by superimposing a code (voice) on top of the signal. The reverse is to demodulate, or to remove the fixed signal and have the voice play back. For many years, this has been an effective way to communicate over long distances, both using wires and radio waves.

The following definitions are some of the basic terms used with modem communication:

Baud An early measurement of how fast a modem can send data. Early modems transmitted data at a speed equal to the baud rate (one bit per cycle). Today’s high-speed modems use more tones to send more data; therefore, data transfer exceeds baud rate. Baud is limited to 2400 cycles per second. Baud rate is limited by the capability of copper wires to transmit signals.

bps Bits per second—the speed that a modem transmits data. Typical rates are 14,400, 28,800, 33,600 and 56,600 bps. This represents the actual number of data bits that can be transmitted per second.

Bulletin Board Service (BBS)

Software that allows connection by a remote computer. BBSes offer the ability to post and retrieve messages, and to upload and download files. Some BBSes offer the opportunity to chat live with other members who are online at the same time.

Conferences Different areas of conversation in an email system, which are topic-specific rather than individualized.

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Download The ability to transfer a file from a remote computer to a local computer. When downloading, you are receiving a file.

IP Internet Protocol – The protocols used to define how data is transmitted on the Internet.

IP Address Internet Protocol Address – A unique 32-bit IP address that identifies every network and host on the Internet. A host is defined as the TCP/IP network interface within the computer, not the computer itself – a computer with two network cards will have two IP addresses.

ISP Internet Service Provider – A host computer that you can dial into via a modem and connect to the internet.

Logging On When connecting to a remote computer, the host computer (the one that is called) must give permission to connect. The process of sending the appropriate information to sign on is called logging on. Often a user name and password are required.

Modem A modem is a telephone for a computer. It consists of a circuit board and is installed internally, as an expansion card (internal), or comes in a separate case that is connected to a COM port (external).

Offline The computers have disconnected and transmission of data is not possible.

Offline Reader A program to display email messages that have been downloaded to a computer.

Online When two computers are connected and transmission of data is possible.

Protocol A set of rules governing the transfer of information.

Settings The settings required by the telecom software in order for data to be transmitted. Usually 8-bits, no parity, 1 stop bit—8N1—will work. Some BBSes require a special terminal emulation, such as VT100, ANSI-BBS, or even TCPM.

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Sysop The system operator of a small BBS. (Pronounced sis-op.)

TCP/IP Transmission Control Protocol/Internet Protocol – the name given to a collection of protocols that were designed in the 1970s for use on the large-scale, mixed-platform that became the Internet.

Telecom Software An application that allows two computers to communicate. Both computers must use either the same or compatible software for communication to take place.

Telecommunication The ability to transmit data over phone lines to a remote computer.

Upload The ability to transfer a file from a local computer to a remote computer. When uploading, you are sending a file to another computer.

Communication

There are two basic problems when using modems to transmit data. Computers transfer data via parallel wires or buses. Modems use serial communication—telephone systems use only two wires.

Serial and Parallel Communication

The second problem is that telephone and radio systems use analog signals (based on a waveforms) and computers use digital signals (on or off).

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Analog and Digital Signals

A modem resolves both of these problems by acting as an A/D converter (analog/digital) and modulator/demodulator. An analog modem uses the RJ-11 connector better known as the phone jack.

Serial/Parallel Conversion

The electronics industry uses a standard chip to make the change from eight-bit wide digital information (parallel) to one-bit wide digital (serial) information. This chip is called a UART (Universal Asynchronous Receiver Transmitter). The original UART chip developed by IBM was called the 8250. While this chip was very common, the chip used today on virtually all modems is the 16550A.

The MSD utility that comes with DOS, Windows 3.x, and Windows 9x (Windows Device Manager) easily identifies the presence of the UART chip in a computer. From the MSD main menu, select COM Ports. The following graphic shows a typical MDS screen with the UART chip identified.

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MDS Utility—COM Ports

Digital Communication

Conversion of data from parallel to serial is only the first step. The digital information must be broken into packets that allow the receiving computer to distinguish one byte from another. Modems employ synchronous or asynchronous communication to resolve this problem.

Synchronous Communication

Synchronous communication is a form of communication in which blocks of data are sent at strictly timed intervals. To initiate the block of data, a series of synchronization signals are sent at the beginning of each data block. Once synchronization is established, block after block can be sent. Synchronized transmissions provide for high-speed data communication and are reserved for intelligent modem systems. All error correction must be handled before the data is sent.

Asynchronous Communication

The second form of transmission is asynchronous communication, a form of data transmission in which the length of time between characters may vary. Timing is dependent on the actual time it takes for the transfer to occur, as opposed to synchronous communication, which is timed rigidly by an external clock. To establish the timing, two additional bits are required. These bits are called the start bit (to initiate the sequence) and the stop bit (to terminate the sequence.)

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Parity

In the days of unreliable memory, an additional chip was added to provide for error checking. That chip was called a parity chip and provided the parity bit. In the chapter on memory, we discussed how the parity bit works. Modem communication adopted the concept of using parity as a way of error checking each byte of data transmitted. With asynchronous communication, packets have an optional parity bit that is used for error detection. The receiving port uses the parity bit to verify whether the data is good or bad. There are two types of parity, let’s review them.

Even parity: The sending computer counts the ones in the data part of the packet, if the number is even, it will set the parity bit to zero. Now the total number of bits containing a one is even. If the number of ones in the data part of the packet is odd, it will set the parity bit to one; once again, making the total number of bits containing a one even. When the packet is received, the receiving port counts the bits and compares the number to the parity bit. If the count does not match the parity bit, an error has occurred and the data will have to be resent.

Odd parity: The same except that the total number of bits must be odd.

Parity bits are optional! The quality of data transmission and phone lines has improved to the extent that parity bits are no longer required. However, if data accuracy is critical and/or phone line quality is questionable, use parity.

Modem Hardware

Now that we’ve seen how modems work, let’s look at the hardware involved.

RS-232

We have already introduced the concept of COM ports in an earlier chapter. External modems are physically connected to a computer by a standard COM serial port. An organization called the Electronic Industries Associations (EIA) created the RS-232 standard for managing the way that data is transmitted and received via these standard ports. RS stands for Recommended Standards. RS-232 is the revision that is applied to serial ports. This standard defines the mechanical, logical, and electrical interface between Data Terminal Equipment (DTE—the computer) and Data Carrier Equipment (DCE—the modem).

RS-232 describes signals, not the actual plug used to transmit and receive the signals. The following table lists the signals and what the abbreviations stand for.

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RS-232 Signals

RTS Request to Send

CTS Clear to Send

DCD Data Carrier Detect

DSR Data Set Ready

DTR Data Terminal Ready

RI Ring Indicator

RS-232 cabling and connectors are based on standard 9 and 25-pin DB connectors. The connectors on the back of a computer used for COM ports and RS-232 communication are the male 9 and 25-pin connectors. Do not confuse the 25-pin RS-232 connector with the 25-pin female connector used for printer ports.

Telephone Lines

When speaking of telephone lines, we are talking about switched networks. This means that in order to make a connection between two phones, a series of switches must be properly aligned. In the early days of telephones, these were true switches. Today, they are electronic switches.

Standard telephone lines that we use every day are based on analog signals. Analog signals are measured based on the frequency at which they operate. The unit of measurement used by phone companies is called baud rate or cycles per second. Due to the limits of the cabling, the maximum speed or frequency that can be achieved is 2400 baud. Remember, telephone lines were designed for voice communication and modem communication had to be adapted to used them.

Connecting a modem to a telephone line is as simple as connecting a telephone extension. They both use the same RJ-11 wiring and connectors. If you look closely at these connectors, you will find that they can use either two or four wires. The two-wire version is used for standard connections. The four-wire version is commonly called an RJ-12 connector and can be used to connect two telephones lines. Two terms that you will need to understand are half-duplex and full duplex.

Half duplex: A signal can flow in two directions, but only one at a time. RJ-11 lines can only be used for half-duplex communication.

Full duplex: A signal can flow in two directions at the same time. RJ-12 connections are used for this type communication. Serial devices cannot transmit in full-duplex mode.

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Telephone companies are slowly replacing the old voice lines with the new digital technology. These lines are called ISDN (Integrated Service Digital Network). ISDN is a digital communication system now used throughout the world of computers. The advantage of ISDN is its speed (64,000 bits per second).

You can access ISDN by installing the appropriate expansion card and software in a computer.

Modem Installation

Installing a modem has become a very simple process. If the modem doesn’t work, look for COM port and IRQ conflicts. Let’s walk though the installation process for both internal and external modems.

Modem Card

As with installing any card or internal board, remember to take the proper precautions for electrostatic discharge and, of course, back up your data before you open the computer case.

Document: Check the current IRQ settings and I/O addresses in the computer. Make a note of available IRQs and addresses.

IRQ and I/O settings: Set up the modem board for available IRQ and I/O settings. This may require changing jumpers. If COM1 and COM2 are in use, the board may be configured using COM3 or COM4 with another available IRQ. Plug and Play (Windows 9x compatible) boards may not require this step because they will automatically detect and configure the IRQ and port settings.

Install the board: Physically install the board in an available expansion bus slot.

Set up the software: The computer must know how to find the new modem. If using COM1 or COM2 with Windows 3.x, it will be automatically detected. If using COM3 or COM4, the Windows SYSTEM.INI file section [386Enh] will have to be updated. In Windows 9x, the Add New Hardware Wizard will usually find the modem and set it up. If you wish, or the wizard does not find the correct modem, you can choose “Select your modem from a list.” This includes all drives provided by Windows or you can select the “Have disk…” option, which will direct the wizard to the CD-ROM or A: drive that contains the drivers provided by the manufacturer. In either case, the wizard instructions are simple and easy to follow. In a Windows 3.x setup—assume the modem is set to COM3 and IRQ5.

Setup command set: Any software that will access the modem must know the correct command set to use. This means identifying the type of modem so the software will use the correct AT commands. When all else fails, try Hayes-compatible or Standard modem.

Document: Write down all the new settings and changes.

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External Modem

External modems are the easier to install than internal boards. External modems convert analog data to digital data. The computer handles the parallel to serial conversions through its COM port (the UART chip).

Connect to a COM port: Choose either COM1 or COM2. Be sure to confirm that the COM port you are using is assigned to the connector on the computer. If the computer is using a serial mouse, it too will be using one of the COM ports and a potential for a conflict exists. You can also use COM3 or COM4 if they are properly installed and configured.

Plug in the cabling: Connect the modem to its power source and to the computer. You will also have to connect a phone line (RJ-11) from the wall jack to the modem.

Software: Configure the software to select the required COM port and the type of modem (command set).

Modem Speeds

When installing and using a modem, the primary consideration is speed. The multimedia of the World Wide Web requires far more speed than the simple data transfers of just a few years ago. Modem speed is measured in baud and bps.

Baud Rate

As mentioned earlier, baud rate refers to how fast a modem can transmit data. Technically, the baud rate is the number of voltage or frequency changes that can be made in a second. A modem that is working at 1200 baud means that the basic carrier frequency has 1200 cycles per second. Due to restrictions imposed by the physics of the wiring, a dial-up phone line can go up to 2400 cycles, a baud rate of 2400.

If each cycle were one bit, then the fastest that data can be transmitted would be 2400 bits per second. However, by using different types of modulation, more than one bit can be transmitted per cycle. Earlier modems used the baud rate to measure their speed. Do not confuse baud with bps.

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Baud

Bits per Second (bps)

When comparing modems, we first look at the maximum speed at which it can transmit data. Modem speeds are measured in bps (bits per second). If a modem modulates one bit for each baud cycle, then the modem speed is 2400 bps. If a 2400-baud modem modulates two bits for one cycle of time, then the modem is said to have a speed of 4800 bps (not a baud rate of 4800). If four bits are modulated within one cycle, then a modem speed of 9600 bps is achieved.

Fax/Modems

The technology for faxes has been around for a long time, long before computers. This was the first technology to transmit images digitally. Initially, there were no standards for transmitting and receiving. This presented a real problem, as the only way to use the technology was to have two machines manufactured by the same company. Ideally, both machines would be identical. Eventually, a European committee (CCITT) developed standards for fax transmission. Today, these standards are compiled into four groups. Groups I through III are analog standards. Group I and II are relatively slow and unacceptable by today’s standards. Group III is the standard used on most fax machines and fax modem expansion cards. Group IV is a new digital standard. Since it requires the use of digital phone lines, its growth and acceptance is slow in coming.

The maximum transmission rate for a FAX is 14,400 bps. Although modems sold today are rated at 56 Kbps, most (if not all) include full fax capability at 14,400 bps.

Information Transfer Protocols

Communication is all about protocols. In order to ensure clear and clean communication without any errors, the device on each end must follow a very strict set of rules. If either device violates any of the rules, communication will fail. These rules are called file transfer protocols. Protocols can be subdivided into two groups based on how they are controlled. The two groups are hardware-based protocols and software-based protocols.

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Hardware Protocols

Hardware protocols are based on the RS-232 standard. They take advantage of the wiring to send control information to the modem. If you are using an external modem, you may have noticed all the lights on the front. If you look closely, you will see the names of the various lights such as CTS (clear to send) and DTR (data terminal ready). During modem activity, these lights will flash. When these lights are on, you are seeing an indication of the hardware protocol activity. Internal modems don’t have the lights, but do use the protocol. Some software programs will emulate the protocol signal activity on the screen for you.

Software Flow Control

When using software to control the flow of data, special control codes are sent to and from the modem. There are three common protocols for flow control:

XON/XOFF – This protocol uses special control characters to start and stop the flow of data.

ACK/NAK – This protocol uses ASCII characters to represent ACKnowlege and NotACKnowledge. This is typically used as a form of error checking. The sending modem will send data and the receiving modem will acknowledge or not acknowledge the receipt of the data.

ETX/ACK – This is a simpler form of the ACK/NAK protocol. It is based on timing. If the receiving modem does not acknowledge receipt of the data within a given time period, an error is assumed by the sending modem.

Data Compression Protocols

Data compression is a means of shrinking files into smaller packets. This allows large files to be transferred on low-capacity media (for instance, floppy disks) or to be more quickly sent over data lines, since the file size has been reduced. Modem data compression algorithms are virtually identical to the ones used in ZIP files. The important point to remember is that with modem compression both modems must use the same method for compression and decompression. The CCITT and MNP (Microcom Networking Protocol) provide standards for both data compression and error correction.

Error Correction Protocols

The following are several error-correcting file transfer protocols.

ASCII

The ASCII protocol is the simplest of all modem protocols. It uses the standard ASCII character set to send data that is similar to sending data to an early dot-matrix printer. While this protocol is simple and can be used by any modem, it does not have any form of error checking. Sending large files and files that contain critical data is not recommended with this protocol.

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Kermit

Kermit got its origins in the academic world. It was designed to transfer files between a large mainframe and microcomputers at Columbia University. This protocol is rarely used today.

Xmodem

Xmodem is the next level protocol. The advantage of Xmodem is that it includes error detection, which makes it more suitable for transferring program files. This is a public domain protocol designed for modems transmitting in the 300 to 1200 bps range. It transfers data in 128-byte blocks with one parity bit. Because of the large data blocks, this form of error checking isn’t perfect. If two errors were to occur, they could cancel themselves by the first error changing the parity bit and then the second error changing it back. For all practical purposes, Ymodem and Zmodem have replaced Xmodem.

Ymodem

Ymodem is next in the series of modem protocols. It provides two advantages over Xmodem. First, it is faster and second it uses 1024-byte data blocks.

Zmodem

This is today’s protocol of choice. It combines all the good attributes of Xmodem and Ymodem plus includes a better error correction algorithm.

Establishing a Connection

Did you ever wonder what all that noise is when modems or fax machines begin to communicate? Well, they are handshaking or negotiating the rules (protocols) of communication. Since not every modem and computer is the same, there must be some way for the two machines to determine how to communicate. That is exactly what happens in that short burst of information between the two modems. Decisions are made as to what speed to transmit (the fastest speed of the slowest device), how the data will be packaged, and who controls the transfer. If both machines cannot satisfy any of the parameters, the negotiations will fail and both parties will disconnect.

Tip: If you experience communication difficulty between two modems, be sure that you have not limited one of them to parameters that the other is unable to meet. For example, if one modem has a minimum speed restriction imposed by the software, it may need to be changed before it can communicate with other modems.

Modem Standards

As with every other communication device, standards are needed to assure that both sides “speak the same language.” Modems have their own set of standardized communication conventions.

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Modulation Standards

Modem standards begin with modulation. If both modems are not using the same modulation technique, they will not be able to communicate. The three popular methods are: FSK – frequency-shift keying, PSK – phase shift keying, and QAM – quadrature-amplitude modulation.

Data Transmission Standards

When modems were an emerging technology, there were no standards. The only way to insure data transmission was to have identical modems on each end. Most manufacturers were making proprietary modems, which made compatibility a real issue. Today, modems comply with several standards. Modem standards evolve either by acceptance of a particular manufacturer’s standard or by committee. A good example of this is the 56K modem. Both Rockwell and US Robotics promoted their standard for 56K communication. Each was incompatible with the other. Finally, the CCITT stepped in with the V.90 standard. This is a compromise and is the standard today. The following is a summary of some of the most common standards for modems:

The Bell 103 Standard – This is a 300-bps standard, based on FSK modulation. Most modems can communicate with this standard, but due to its speed, it is obsolete.

Bell 212A – This standard operates at 600 baud, but can transmit 2-bits per baud or 1200 bps.

MNP Standards

MNP (Microcom Networking Protocol) provides standards for end-to-end error correction. The Micron Company released these standards to the public domain. They are capable of detecting transmission errors and requesting retransmission of corrupted data. Although these standards were released to the public domain, they did not gain much popularity. They are still supported by many modem manufacturers, however.

Today’s Modem Standards

The Consultative Committee on International Telephony and Telegraphy (CCITT) is the leading communication standard organization. They have developed what is commonly known as the “V” standard. The “V” standards specify modem speed, data compression, error correction, and fax specifications. The following is a summary of the CCITT “V” standards:

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CCITT Standards

Speed bps Standard Notes

2400 V.22bis An old standard. Sometimes included with the purchase of a computer.

9600 V.32 Sometimes included with the purchase of a computer.

14,400 V.32bis The current standard FAX model.

19,200 V.32terbo Not officially a standard yet. Will only communicate with another V.32terbo.

28,800 V.FastClass Not official.

28,800 V.34 Improved V.FastClass. Backwards compatible with earlier V. modems.

57,600 V.42 Backwards compatible with earlier V modems – error correction standard.

56,600 V.90 56K modem standard – resolved competition for standard between US Robotic X2 and Rockwell

K56 Flex standards.

Note: bis means the second revision of the standard.

56K Modems

Phone lines are capable of carrying 56 Kbps of data, however, conversion from analog to digital and back comes with a price. That price is a speed limit of 33.6 Kbps. Due to the fact that current phone systems are predominately digital, it is possible to transmit (in some instances) at a full 56 Kbps in one direction. The return data, however, is still limited to 33.6 Kbps. For these reasons, it is unlikely that you can achieve a full data transfer rate with a 56K modem. Noise on the line can further reduce this figure. In order to achieve the best performance, the following conditions must be met:

• Digital to analog conversion should be limited to once within the network. Each time the conversion must be made slows the communication process.

• The host must be connected digitally.

• Both modems must support the 56K technology.

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There are currently three 56K modem standards, K56flex, X2 and V90. Unfortunately, these standards are not compatible at 56K, so in order to achieve the highest possible speed, both modems must use the same standard. Several companies developed the K56flex standard and US Robotics developed the X2. Currently, the V90 standard is replacing both the K56flex and the X2 and most 56K modems can be upgraded to this standard. If you have a 56K modem and want to upgrade to V90, check the manufacturer’s web site for instructions and downloading of any appropriate software.

Here is a helpful chart you can use to review the different types of modems available for Internet connection:

Type of Modem Definition

Analog modem The most common modem. It connects via a single phone line and given ideal connections, can reach speeds of 56 Kbps.

ISDN (Integrated Services Digital Network) modem

It requires two phone lines, and given ideal connections, can reach speeds of 128 Kbps.

DSL (Digital Subscriber Line) modem It uses regular phone lines but the switching station must be close by. Its speeds can reach 9 Mbps.

Cable modem It works with the coaxial cable used by the cable company. Speed is affected by the amount of users on a subnet, but it can reach 2 Mbps.

AT Commands

Just like the early computers, which needed DOS commands to tell them what to do, modems also need commands. Programmers needed a standard command set so they could incorporate the use of modems in their software. Unfortunately, there are no true standard command sets for modems and manufacturers are free to create their own. However, one set of commands has been accepted as a “standard.” Most modems today are Hayes-compatible. In the early 1980s, Hayes developed the AT command set.

These commands are very useful as a diagnostics tool for today’s computer professional. To use these commands, make sure the communication software is loaded and the computer is in terminal mode. If you are using Windows 9x, it is called hyper-terminal. With hyper-terminal, you will need to “pretend” that you are setting up a new connection and enter a fake phone number (I use 555-5555), but cancel the screen that wants to dial-

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out or connect. Unless the modem is set up to auto connect (online mode) it will be in command mode and ready to accept AT commands. The AT commands are entered in the ATXn format. AT always precedes the command and Xn is the variable. The following table lists some of the more useful AT commands used by computer professionals:

Hayes AT Commands

Command Function

AT IF you enter this command by itself, the response will be OK if the modem is running.

ARL3 High speaker volume.

ATA Goes off-hook and attempts to answer a call.

ATD This command is used to dial a number.

ATE0 Turns off the echo command.

ATE1 Turns on the echo command.

ATH Takes the phone off the hook.

ATH, ATH0 Hangs up the modem.

ATL2 Medium speaker volume.

ATM0 Turns the speaker off.

ATM1 Turns the speaker on.

ATM3 Turns speaker off during dialing and while receiving the carrier.

ATZ Resets the modem.

Troubleshooting

It can be very frustrating when a modem does not function as expected. However, follow these simple guidelines to determine whether the modem is broken, or if something else is the culprit. The trick to resolving a modem problem is to isolate the problem to either the modem or the software that controls it. Most operating systems, such as Windows 9x provide modem diagnostic programs. Run them. You can also use DOS or a terminal emulation program and enter some AT commands as suggested above. If the modem responds to AT commands, the hardware is operating. The following table suggests some solutions to modem problems:

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Modem Troubleshooting

Possible Cause Possible Solution

Was new hardware added to the computer?

If yes – check for hardware conflicts (IRQ, I/O, and DMA).

Was any new software added to the computer?

If yes – If the software is used to drive any communications, it may have changed some default settings or taken control of the modem for itself.

Operating system or software program can’t find the modem.

The modem configuration may have changed. Make sure the software is looking at the correct port.

Reconfigure or reinstall the software (may be a corrupt driver).

Local modem is having transmit/receive issues

Test the transmit and receive function with a loopback test

Modem works sporadically. Could be a hardware conflict. What other programs are running when it fails?

Check the phone lines.

Modem does not dial out Check the cabling.

The modem configuration needs adjustment.

Modem does not hang up the phone line.

A power surge (lightning) can cause this problem. If manual disconnect and reconnect allows the modem to work, have the modem repaired or replaced.

External modem isn’t functioning correctly

Check the RS-232 cabling to make sure that it isn’t faulty.

Use a loopback plug to test the serial port.

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Summary

This chapter covers modem concepts that enable us to communicate with the world. The following information summarizes the key points of this chapter:

• Modems have become standard computer equipment.

• Modems convert parallel digital data to and from serial analog data.

• Modem speeds are based on bps (bits per second).

• CCITT establishes standards for modem communication.

• AT commands are used to manually communicate with and test a modem.

• Modems can be installed internally or externally.

• The number one modem problem is IRQ conflicts.

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KEYWORDS Exercise

Define each of the following keywords. Hint: There’s a glossary in the back of this book.

Keyword Definition

ASCII Protocol

Asynchronous communication

Baud

Baud rate

Bps

BBS

Conferences

Download

Even parity

Full-duplex

Half-duplex

Handshaking

IP

ISP

IP Address

Kermit

Logging On

Modem

Modem

Odd parity

Offline

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Keyword Definition

Offline Reader

Online

Protocol

RS-232

Settings

Synchronous communication

Sysop

TCP/IP

Telecom Software

Telecommunication

UART

Upload

Xmodem

Ymodem

Zmodem

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Review Questions Chapter 12

1. What kind of signals do telephones use? Computers?

2. What is the purpose of a modem?

3. Which AT command is used to take the phone off the hook?

4. What is the difference between baud and bps?

5. What is the name of the chip that converts data from parallel to serial?

6. Name three transfer protocols and describe the differences between them.

7. What is Zmodem? What are its advantages over other protocols?

8. What are AT commands and how can a computer technician use them?

9. Explain the difference between half-duplex and full duplex. What makes them different? Where or when are each used?

10. What is the difference between synchronous and asynchronous communication?

11. Why are fax standards different than modem standards?

12. What is a null-modem cable and when would it be used?

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Chapter 13 – Portable Systems

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Chapter 13 – Portable Systems

A way of moving information around or better yet, taking it with you is by using portable computers. In the early days of computers, we simply took a disk from one location to another. Now, if you travel a lot, you can take your computer. Portable computers work and act just like desktops except for their small size. This chapter is going to address the issues that make a portable computer different from the desktops we have been studying.

Types of Portables

Portable computers describe luggables, laptops, notebooks and sub-notebooks (palmtops). Palmtops are more frequently referred to these days as Personal Digital Assistants or PDAs for short. When laptops and notebook computers were first introduced, they were not very popular because of their equipment limitations (size, weight, and inability to add hardware). Today’s portable systems are virtually desktop computer counterparts. Many companies provide traveling employees with portable computers as their primary systems.

Today three basic configurations describe portable computers: laptops, notebooks and sub-notebooks.

Laptops

There were two technologies whose advancement paved the way for the development of portable computers. The number one problem with portable designs has always been around how to power them. The advancements in battery technology and the advent of functional large screen LCD displays opened the door to the development of useable portable systems. These units featured all in one AT compatible computer boards and the system board included the I/O and video controller functions. Laptops usually feature a folding LCD display and a built-in keyboard. They also use an external power supply and a removable, rechargeable battery. Today’s laptops have large hard drives (10 to 20 GB and climbing), a CD drive, and floppy (often the latter two are interchangeable plug-ins). If you need to replace a part in a laptop, it is generally required that the replacement come from the manufacturer.

When laptops originally appeared on the market, they were the smallest portables made. Today they have become high-end machines that offer features and performance comparable to a desktop system. Technological advances have even made them much lighter, contradicting the term “luggable.”

Notebooks

Advancements in IC (Integrated Circuit) technology allowed computer circuitry to be reduced even further and the Notebook computer was born. Notebooks are roughly 8.75”d x 11”w x 2.25”h and designers are working to decrease the size and power consumption of these units even further. The reduction in size does come at a cost however, and notebooks typically come with smaller and less capable displays and keys.

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A wide variety of specialty items have appeared on the market intending to overcome some the notebook’s shortcomings. Docking ports are one such item.

Docking ports (also known as docking stations) bring the portable world and the desktop world together. They are specialized cases into which the entire notebook can be inserted. This allows the notebook to be connected to a collection of desktop I/O devices such as full size keyboards and CRT monitors. At the very least, a docking station will provide an AC power source for the notebook. On the high-end, they will allow for the addition of full size expansion cards such as modems and network adapter cards. Docking stations are highly proprietary items and are designed for use with specific computer models. They also function as surge suppressors. They are useful to the user who is on the go, whether only to and from the office, or around the world. The user can maintain only one computer system and avoid the necessity of transferring information between two systems.

It is not necessary to have a docking port to use a portable computer with a full sized keyboard, pointing device, and monitor. Most portables have standard connectors for these peripherals. Be aware that you may have to connect the devices before booting the computer.

Sub-Notebooks (Palmtops)

Even smaller than the notebooks are the sub-notebooks, also known as Palmtops. These tiny systems are reduced to the size of 7”w x 4”d x 1”h but are rather limited in function to reach this size. As notebooks have decreased in cost and weight, palmtops have been losing market share and popularity. Special operating systems have been developed just for the special computers. Windows CE is an example of such an operating system.

Personal Digital Assistants (PDA)

These devices are the modern version of the palmtop. Their dimensions are roughly the same, but their functions far outweigh their predecessors. These handy devices are perfect for the businessperson on the go, because they are loaded with scheduling capabilities. In addition to calendars, address books, etc., the high-end PDA devices include specialized versions of software, such as Microsoft’s Word.

Some PDAs have miniature keyboards, while others use a stylus for entering data. The stylus can be used to select letters and numbers to be entered, or you can write the letter or number and it will enter it that way. The better ones also include infrared or USB ports (or both) that can be used to synchronize your desktop system (or laptop for that matter) with your PDA. The high-end versions are also Internet capable.

Not all of these devices are created equally however; you can expect to spend about $500 on a PDA that has all the bells and whistles. Keep in mind that the low-end versions can turn out to be nothing more than an electronic address book.

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Computer Cards (PCMCIA)

In order for laptop and notebook computers to have the same expandability associated with desktop computers, the Personal Computer Memory Card International Association (PCMCIA) established several standards for credit card sized expansion boards that fit into small slots on laptop and notebook computers. PCMCIA is also referred to as the PC-Card Bus, or just PC Card for short. The PCMCIA standards have revolutionized the mobile personal computer because they now have the ability to add memory expansion cards, SCSI devices, communication hardware (i.e. modems and faxes) and many other devices which were previously unavailable for laptop and notebook computer users.

As with everything, compatibility problems surfaced along with the development of the PCMCIA card for portable computers. To overcome these incompatibilities, PCMCIA standards were created. The table below outlines the four types and their guidelines or standards.

PCMCIA Types

TYPE Standard Description

Type I This is the original computer-card standard and is now referred to as the Type I standard. These slots work only with memory expansion cards. Type I can handle cards that are 3.3mm thick.

Type II

Type II cards support most types of expansion devices (like communication hardware) or network adapters. Type II can accommodate cards that are 5mm thick.

Type III The Type III slot is primarily for computers that have removable hard drives. This standard was introduced in 1992. They are 10.5mm thick, however they are compatible with Type I and Type II cards. Two of these cards can be connected at one time.

Type IV

Type IV slots are intended to be used with hard drives that are thicker than the 10.5mm Type III slot.

The PC card itself usually is sealed in a metal case except where the interface to the PCMCIA adapter is located, which consists of 68 tiny pinholes. The other end of the card may contain a connector for a telephone line, a network drop cable or another external device.

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PCMCIA (PC-Card) is part of the plug and play standard. To be plug and play compatible it means you should be able to add components without shutting off or rebooting the computer. In short, PCMCIA buses are not configured with ju