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Basic Hardware Overview

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System Case

• The major hardware components of the computer, as opposed to the I/O devices and other peripherals, are housed in the case. – Also known as chassis or enclosure or system unit.

• The case helps keep the components clean and cool.

• It can also provide some shielding to undesired outside voltages.

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Case with side panel removed.

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More than just a box

• At first the case strikes one simply as a container, but it has some structure.

• If one is building a PC, the case has to be coordinated with the motherboard one chooses.

• The case will also determine how much access there is to the front and back of the PC – the number of bays, expansion slots and so on.

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• Cases come is various sizes and shapes, known as “form factors”– Micro tower, mini tower, mid tower, full tower,

microATX desktop, and ATX desktop.

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Power Supply

• Computers work by having a value – in binary computers a high or low – represented by some physical quantity.

• The physical quantity is typically an electronic voltage or electronic current.

• Thus we need some part of the computer responsible for supplying electronic voltages and/or currents. This is the power supply.

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Transformer

• Strictly speaking the device known as a power supply does not supply power, it transforms it. The source of the power is a generating station, the power is then delivered to buildings and made available at wall outlets. The power supplied by the outlet must be transformed into the form that is useful for computers.

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AC-DC

• The outlet supplies somewhat high-voltage AC (alternating current) – In the US, the AC supplied is known as 110, it varies

from approximately a positive 156 volts to a negative 156 volts many time a second.

• Computers need low-voltage DC (direct current) – Various components need differing amounts of steady

voltage (12 volts, 5 volts, ±3.3 volts, etc.)

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Caution

• Because of the relatively high voltages coming in and the way in which the transformation is done, power supplies can be dangerous.

• Do not open up a power supply, unless you have been trained.

• Usually if a power supply goes, it is replaced as a unit.

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Power to the components

• The transformed power must in turn reach the components that use it: – The motherboard and the devices thereon– The various drives (floppy, hard disk, CD) – Etc.

• There is a special (larger) connector to the mother board.

• The drives are connected with the smaller Molex connectors and the even smaller Mini connectors.

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Parts of a Power Supply

Molex ConnectorMini Connector

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Motherboard• A circuit is a path or paths which current through

a set of electronic components (resistors, capacitors, transistors, etc.).

• If a number of the components are etched into a semiconductor, this is called a chip.

• If a circuit or circuits are printed onto a board, this is called a circuit board.

• The main circuit board is a computer is known as the motherboard.

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The place to meet• The major components are on the motherboard or

plug into it. • The motherboard has places for processor, cache

and memory to plug into. • These component interface with other components

via the chipset. • The chipset leads to the controllers of various other

components (floppy drive, hard drive, keyboard, mouse, etc) and to expansion slots so that other circuitry can be added making the PC customizable.

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Chipset• Most of the manipulation of data is done by the

processor. The rest is mostly moving data around. And the principle traffic cop is the chipset.

• The chipset allows the storage and input devices to interface with the processor, memory and cache.

• The chipset will determine which processors can be used in the PC, how much cache and memory are allowed, etc.

• Since the chipset interfaces the components with vastly different speeds, it can be crucial is determining a PC’s performance.

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Controllers

• Whereas the chipset is a centralized, generic data-flow manager; controllers are individual, specific data-flow manager that allow one to interface with specific devices.

• Hence one has a floppy controller, a keyboard controller, and so on.

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Buses

• If the motherboard’s chipset and controllers are the traffic cops, then the motherboard’s buses are the streets.

• Since so many devices want to interface with the processor, there is a set of shared channels for information going to or coming from the processor. These are the buses.

• Like streets, they can vary in speed and capacity. There are fast buses for fast devices and slow buses for slow devices.

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BIOS

• The Basis Input/Output System or BIOS is firmware (instructions burned into ROM) that interface between the various hardware components on and plugged into the motherboard and the operating system.

• This layering means that the operating system is not dependent the specifics of the hardware.

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BIOS

• The BIOS is written in ROM because it rarely changes. It may be in EEPROM (Electrically Erasable Programmable Read-Only Memory) so that it can be changed occasionally – flashing the BIOS.

• Being ROM also implies that these instructions are non-volatile not lost when the power goes off. Thus the instructions for starting the PC are written in this way.

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Processor

• The processor, a.k.a. the Central Processing Unit or CPU interprets the instructions it finds in memory (programs) and responds to and modifies (I.e. processes) the information and directs the other components how to respond.

• The CPU is sometimes thought of as consisting of two parts: – The Arithmetic Logic Unit (ALU)

– Control

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Processor

• The processor is the most important chip in a PC – often called the brain of the computer.

• The processor has a lot of contacts called pins which plug into the motherboard and allow electronic information to flow to and from the processor.

• The pins are arranged in rows around the chip’s perimeter in what is known as the Pin Grid Array PGA.

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Processor features

• Two of the main features of processors are their speed and their instruction set.

• Instructions are broken down into their smallest steps and the processor speed determines the amount of time required for one of these smallest steps.

• A processor’s instruction set is the collection of basic things it knows how to do.

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System Memory

• The processor executes instructions. The combination of instructions can be varied – that is computers can be programmed.

• The combination of instructions as well as the data that the processor is currently acting on are held in memory.

• Memory can be distinguished from storage by its intimate connection to the processor and by its volatility – data in memory, Random-Access Memory (RAM) is lost when the power goes off.

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Cache• There are two basic types of RAM

– Static RAM (SRAM) is fast but expensive– Dynamic RAM (DRAM) is slow but cheap

• The processor’s speed is faster than main memory which is made of DRAM. A special unit of faster SRAM memory works even more intimately with the processor than memory is known as cache.

• Cache is a very sophisticated game of guessing what instructions and data the processor will next need and placing it in the location that can be accessed more efficiently.

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Storage• Memory is essential (otherwise computers would not

be programmable), storage is simply a convenience and was not a part of the earliest computers.

• But without storage the programs and accompanying data would have to be entered anew each time.

• Storage is nonvolatile (keeps the information) without needing power – so that programs and data can be kept from execution to execution, day to day, year to year.

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Hard disk drive

• The main storage device is the hard disk. • The hard disk uses a magnetic material.

The magnetic property can be placed in two states corresponding to 1’s and 0’s.

• The magnetic state can be determined (read) or set (written) by electronic means but the state can be maintained without constant electric power.

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Floppy Disk Drive

• Hard drives are usually permanent within the case, a storage medium that can be taken out of the case is said to be removable. (Some hard drives are removable.)

• The earliest storage in PCs was a removable magnetic medium known as the floppy disk.

• Early on floppy disks shrunk in size and gained in capacity but this stopped at 3-1/2 inch floppy disk with 1.44 MB of storage that is standard today.

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CD ROM Drive• CDs (Compact Disks) are an optical medium of storage

that has become standard in PCs. • A standard CD has thousands of times the capacity of a

floppy disk. • Originally CDs were Read Only (CD-ROM), written

by the manufacturer and useful as a software delivery system.

• As the amount of data users wanted to be portable grew, a recordable CD (CD-R) filled the void. But it had the limitation of being Write Once.

• Finally the rewritable CDs (CD-RW) became available.

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Keyboard

• Early computers inputting was done by plugging wires in boards or flipping switches or paper tape or punch cards. But the keyboard made data entry user friendly.

• PCs have always had generic connectors to plug in devices so that users could adapt them to various purposes, but the keyboard is so standard it soon had a designated connector and controller on the motherboard.

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Mouse• The mouse was not a standard input device in early PCs.

(They were initially frowned upon by people who considered themselves serious computer users.)

• But the user friendly graphical user interface (GUI) approach made using a computer more palatable to most users and it soon became standard with its own designated connector.

• The trend for devices becoming standard and having designated connectors has changed somewhat recently with the introduction of the USB (universal serial bus) and USB keyboards and USB mice.

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Displays

• The earliest display devices were lights or light-emitting diodes (LEDs). However, any significant amount of binary output is difficult to read.

• The monitor was an early standard output device. Early monitors were monochrome Cathode Ray Tubes (CRTs) – the same basic technology as television.

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CRTs

• A stream of electrons (a cathode ray) is aimed toward the screen which is coated with various phosphors; the electrons transfer their energy to the phosphors which then glow

• There are phosphors for red and green and blue which can be combined to make all other colors.

• An individual speck is known as a pixel and the number of pixels determines the screen’s resolution.

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LCDs• CRT’s are OK for desktop computers, but laptops

require something smaller and lighter; they need “flat panel displays”

• The most common flat panel display is the liquid-crystal display (LCD)

• Liquid crystals are molecules said to be in a state between liquid and solid.

• Their optical properties are affected by electric current or fields, hence their use as displays: watches, laptop screens, etc.

• Flat panels are replacing CRTs even on the desktop.

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Expansion Cards

• The video card – extra circuitry needed to interface with the monitor – added to the capability of PCs.

• In order to make PCs customizable, they have expansion slots – places where extra circuit boards called expansion cards can be added.

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NIC

• PCs were initially stand-alone devices. But networking proved to be important and crucial. The PC’s expansion slots allowed a user to add a Network Interface Card (NIC) to allow the computer to exchange information with other computers.

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Ports

• In addition to expansion slots which allowed one to add circuitry to interface with peripherals, PCs also had two standard interface paradigms that if a device could use these, additional circuitry was not needed. The device could just be plugged in.

• These places to plug theses devices are called ports and the two standards developed are serial connection and parallel connection.

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Serial Communication

• A serial connection sends information over the line one bit at a time. It is a simple way to send information in or out of the computer, but is not as fast as other ways the computer can communicate. Serial connections are typically used for devices such as mice and modems.

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DB Connector

• While serial data flows one bit at a time and can flow along a single wire. There’s more to communication than just flow of information. The two devices must agree to communication, so there are additional wires needed.

• A generic serial connector is the DB connector. (DB – databus)

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Parallel Communication• A parallel connection is faster than a serial one

because it sends many bits in parallel. The advantage of this is that it is faster, but the disadvantage is that it is more complicated to do. Parallel connections are used most often for printers and removable storage drives, which need more speed than serial peripherals.

• Recently advances in serial connections have made them competitive with parallel connections. And devices such as printers conventionally thought of as strictly parallel devices are no longer thus.

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References

• http://www.pcguide.com/

• http://www.webopedia.com

• http://www.whatis.com

• PC Hardware in a Nutshell, Thompson and Thompson

• A+ Certification: Exam Guide, Meyers and Jernigan