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How Do Computers Work?How Do Computers Work? A Gentle Introduction A Gentle Introduction
How Do Computers Work?How Do Computers Work? A Gentle Introduction A Gentle Introduction
Poly Pride
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
2
Hardware and Software
• Hardware– the physical, tangible parts of a computer– keyboard, monitor, disks, wires, chips, etc.
• Software– programs and data– a program is a series of instructions
• A computer requires both hardware and software
• Each is essentially useless without the other
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
3
CPU and Main Memory
CentralProcessing
Unit
MainMemory
Chip that executes program commands
Intel Pentium 4Sun ultraSPARC IIIPrimary storage
area for programs and
data that are in active use
Synonymous with RAM
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
4
Secondary Memory Devices
Information is movedbetween main memoryand secondary memoryas needed
CentralProcessing
Unit
MainMemory
Floppy Disk
Hard Disk
Secondary memorydevices providelong-term storage
Hard disksFloppy disksZIP disksWritable CDsWritable DVDsTapes
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
5
Input / Output Devices
CentralProcessing
Unit
MainMemory
Floppy Disk
Hard Disk
Monitor
Keyboard
I/O devices facilitateuser interaction
Monitor screenKeyboardMouseJoystickBar code scannerTouch screen
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
6
Software Categories• Operating System
– controls all machine activities– provides the user interface to the computer– manages resources such as the CPU and memory– Windows XP, Unix, Linux, Mac OS
• Application program– generic term for any other kind of software– word processors, missile control systems, games
• Most operating systems and application programs have a graphical user interface (GUI)
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
7
Analog vs. Digital
• There are two basic ways to store and manage data:
• Analog– continuous, in direct proportion to the data
represented– music on a record album - a needle rides on ridges
in the grooves that are directly proportional to the voltages sent to the speaker
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
8
Analog vs. Digital
• Digital– the information is broken down into pieces, and
each piece is represented separately– music on a compact disc - the disc stores numbers
representing specific voltage levels sampled at specific times
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
9
Digital Information
• Computers store all information digitally:– numbers– text– graphics and images– video– audio– program instructions
• In some way, all information is digitized - broken down into pieces and represented as numbers
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
10
Representing Text Digitally
• For example, every character is stored as a number, including spaces, digits, and punctuation
• Corresponding upper and lower case letters are separate characters
H i , H e a t h e r .
72 105 44 32 72 101 97 116 104 101 114 46
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
11
Binary Numbers
• Once information is digitized, it is represented and stored in memory using the binary number system
• A single binary digit (0 or 1) is called a bit
• Devices that store and move information are cheaper and more reliable if they have to represent only two states
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
12
Binary Numbers
• A single bit can represent two possible states, like a light bulb that is either on (1) or off (0)
• Combinations of bits are used to store values
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
13
Bit Combinations
1 bit
01
2 bits
00011011
3 bits
000001010011100101110111
4 bits
00000001001000110100010101100111
10001001101010111100110111101111
Each additional bit doubles the number of possible combinations
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
14
Bit Combinations
• Each combination can represent a particular item
• There are 2N combinations of N bits
• Therefore, N bits are needed to represent 2N unique items
21 = 2 items
22 = 4 items
23 = 8 items
24 = 16 items
25 = 32 items
1 bit ?
2 bits ?
3 bits ?
4 bits ?
5 bits ?
How manyitems can be
represented by
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
15
Bit Combinations
• Suppose we have three bits … see how different numbers are represented with them
1 0 1 5
22 = 4 0 1+ + = 5
1 1 1 7
22 = 4 21 = 2 1+ + = 7
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
16
Bit Combinations
• Since you were very small, people have told you that you can count up to 10 with your two hands, right?
• Well … you can do better than this …
• With one hand you can count up to 31 …
• With two hands you can count up to 1023 …
• How
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
17
Bit Combinations
0
123
4
20 = 1
21 = 222 = 423 = 8
24 = 16
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
18
Bit CombinationsWhat
number is this??
NOT Showing
SHOWING
!
1
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
19
Bit CombinationsWhat
number is this??
NOT Showing
SHOWING
!
2
NOT Showing
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
20
A Computer Specification
• Consider the following specification for a personal computer:
– 2.8 GHz Pentium 4 Processor– 512 MB RAM– 80 GB Hard Disk– 48x CD-RW / DVD-ROM Combo Drive – 17” Video Display with 1280 x 1024 resolution– 56 Kb/s Modem
• What does it all mean?
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
21
Memory
Main memory is divided into many memory locations (or cells)
927892799280928192829283928492859286
Each memory cell has a numeric address, which uniquely identifies it
Remember this?
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
22
Storing Information
927892799280928192829283928492859286
Large values arestored in consecutivememory locations
1001101010011010Each memory cell stores a set number of bits (usually 8 bits, or one byte)
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
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Storage Capacity
• Every memory device has a storage capacity, indicating the number of bytes it can hold
• Capacities are expressed in various units:
KB 210 = 1024
MB 220 (over 1 million)
GB 230 (over 1 billion)
TB 240 (over 1 trillion)
Unit Symbol Number of Bytes
kilobyte
megabyte
gigabyte
terabyte
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
24
Memory
• Main memory is volatile - stored information is lost if the electric power is removed
• Secondary memory devices are nonvolatile
• Main memory and disks are direct access devices - information can be reached directly
• The terms direct access and random access often are used interchangeably
Meaning Pronunciation
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
25
Memory
• A magnetic tape is a sequential access device since its data is arranged in a linear order - you must get by the intervening data in order to access other information
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
26
RAM vs. ROM
• RAM - Random Access Memory (direct access)
• ROM - Read-Only Memory
• The terms RAM and main memory are basically interchangeable
• ROM could be a set of memory chips, or a separate device, such as a CD ROM
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
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RAM vs. ROM
• Both RAM and ROM are random (direct) access devices!
• RAM probably should be called Read-Write Memory
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
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Compact Discs• A CD-ROM is portable read-only memory
• A microscopic pit on a CD represents a binary 1 and a smooth area represents a binary 0
• A low-intensity laser reflects strongly from a smooth area and weakly from a pit
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
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Compact Discs• A CD-Recordable (CD-R) drive can be used to
write information to a CD once
• A CD-Rewritable (CD-RW) can be erased and reused
• The speed of a CD drive indicates how fast (max) it can read and write information to a CD
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
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DVDs
• A DVD is the same size as a CD, but can store much more information
• The format of a DVD stores more bits per square inch
DVD = Digital Versatile DiskRead More HERE
Meaning and Pronunciation
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
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DVDs
• A CD can store 650 MB, while a standard DVD can store 4.7 GB– A double sided DVD can store 9.4 GB
– Other advanced techniques can bring the capacity up to 17.0 GB
• Like CDs, there are DVD-R and DVD-RW discs
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
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The Central Processing Unit (CPU)
• A CPU is on a chip called a microprocessor
• It continuously follows the fetch-decode-execute cycle:
fetch
Retrieve an instruction from main memory
decode
Determine what theinstruction is
execute
Carry out theinstruction
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
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The Central Processing Unit
• The CPU contains:
Arithmetic / Logic Unit
Registers
Control Unit
Small storage areas
Performs calculations and makes decisions
Coordinates processing steps
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
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The Central Processing Unit
• The speed of a CPU is controlled by the system clock
• The system clock generates an electronic pulse at regular intervals
• The pulses coordinate the activities of the CPU
• The speed is usually measured in gigahertz (GHz)
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
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Monitor
• The size of a monitor (17") is measured diagonally, like a television screen
• Most monitors these days have multimedia capabilities: text, graphics, video, etc.
• A monitor has a certain maximum resolution , indicating the number of picture elements, called pixels, that it can display (such as 1280 by 1024)
• High resolution (more pixels) produces sharper pictures
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
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Modem
• Data transfer devices allow information to be sent and received between computers
• Many computers include a modulator-demodulator or modem, which allows information to be moved across a telephone line
• A data transfer device has a maximum data transfer rate
• A modem, for instance, may have a data transfer rate of 56,000 bits per second (bps)
04/19/23 How Do Computers Work? Part III Dr. A. Sanchez
37
How do you connect to the Internet?
Ethernet vs. ModemWhich is faster? Why?
Requirements?
What is transmission speed measure in?Modems Ethernet56 KBpS 1 – 100 MBpS112 KBpS