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THE SYSTEM UNIT

2

System Units in MicrocomputersSystem Units (system cabinet):container that contain the electronic components of computer system

Types of System Units in Microcomputers

1. Desktop :input and output devices are located outside the system unit

2. Notebook(laptop): input devices located inside the system unit but output device like monitor is outside the system unit.

3. Tablet PC ,there are 2 kinds: 1-monitor is swivels and folds onto keyboard. 2-monitor is attached to system unit and does not have keyboard (supports the use of a stylus or pen to input commands and data )

4. Handheld (like ---PDA),input and output devices are inside system unit.

3

Electronic Data and Instructions

Data and instructions are represented electronically

Computers recognize digital signals

Binary system (0,1)Bit

Byte

4

Binary Coding Scheme

Two state systemOff/on electrical states

Characters represented by 0s and 1s

Three types of schemesASCII-used in microcomputer

EBCDIC-used in large computer

Unicode -16 bit code

5

System Board(mother board)

Connects all components and allows communication between devices

Electronic components in system board:

1. Sockets (provide connection for chips)

2. Slots (provide connection point for cards)

3. Bus lines (provide communication paths)

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Microprocessor

Central Processing Unit (CPU )Two basic components 1. Control unit • Program instructions• Directs flow between memory and ALU• Directs flow between CPU and I/O devices

2. Arithmetic and logic unit

perform arithmetic and logical unit

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Microprocessor Chips

Chip capacities are expressed in word sizes

A word is the number of bits that can be accessed at one time by the CPU

byte=8 bits

32 bit –word----32/8=4-----this mean computer can accessv4 bytes at a time.

Dual-core microprocessor : It is chip can provide 2 separate and independent CPUs , so computer can run 2 programs at the same time.

Parallel processing :divide programs into parts so each CPU could process each part independently

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Memory

Holding area for data, instructions, and information

Types of memory chipsRAM (Random Access Memory)

ROM (Read Only Memory)

CMOS – flexible start-up instructions

Memory • RAM –temporary holding area,

-Volatile - when power shuts off, contents of RAM are lost.

• ROM – Read Only Memory; nonvolatile; user does not change information on ROM

- the factory put instructions and programs in ROM that that need to start computer

• CMOS – unlike RAM ,it is powered by battery

_unlike ROM ,data can be changed

_In CMOS information needed every time computer turned on like current data and time ,…

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Memory

Cache memory :high speed memory located between RAM and CPU ,computer make copy of most information accessed by CPU from RAM and put these information in Cache so results in faster processing results for the user

Flash memory :type of RAM hold data hold data even after computer turn off .It is expensive and used in digital camera and cell phone.

Virtual memory : divide large program into parts saved in hard disk then each part read into RAM when needed .

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System Clock

• Controls speed of systemProduces electrical beats

Expressed in gigahertz

Faster clock speed, faster computer

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Expansion Slots and Cards

Allow for new devices to be added

Plug & play : set of H.W & S.W , it can automatically install card.

Expansion cards are also called …Plug-in boards

Controller cards

Adapter cards

Interface cards

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Commonly Used Expansion Cards

Video cards

Modem cards

Network interface cards (NIC)

TV tuner cards

PC cards

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Bus Lines

Bus lines provide data pathways that connect various system components

bus width : the number of bits travel simultaneously

Two basic categories1. System buses

2. Expansion buses

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Ports

Socket for connecting external devices

Four common portsSerial

Parallel

USB

FireWire

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Power Supply

Computers require direct current (DC)

DC power provided by converting alternating current (AC) from wall outlets or batteries

Desktop computers use power supply units

Notebooks and handhelds use AC adapters

AC adapter

Power Supply Unit

The End of Chapter 6