chapter 03-system unit

8/12/2019 Chapter 03-System Unit

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TTS1033

Concepts and Applications of

Information Technology


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The system unit is the case that houses the

electronic components of the computer

system.

Sometimes called thechassis


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Motherboard

Processor

Memory

Bus Line

Adapter cards

Power supply

PortsDrive bays


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Main circuit board of the system unit

Contains expansion slots,processor chips,

andmemory slots

Also called system board


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The computer does it primary work in a part of the

machine we cannot see.

The control center, called CPU is a highly complex,

extensive set of electronic circuitry that executes stored

program instruction. All computers, large and small must have at least one CPU

CPU consists of two parts : the control unit and

Arithmetic/logic Unit


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The CU contains circuitry that uses electrical

signals to direct entire computer system to

carry out, or execute stored program

instructions. The CU not executes the program

instructions, but just directs other part of

system to do so. The CU must communicate

with ALU and memory.


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The ALU contains the electronic circuitry

that executes all arithmetic and logical

operations

The ALU performs four kinds of arithmeticoperations. comparison, and logical

operations


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This section will explain the way CPU

executes one instruction in a computer

program. Many PC can execute instructions

in less than one millionth of a second.

Each time the CPU executes an instruction, ittakes a series of steps. The complete series

of steps is called a machine cycle.

A machine cycle can be divided into two

smaller cycles. These are :

instruction cycle.

execution cycle.


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Fetching

Before the CPU can execute an instruction, the

control unit must retrieve or fetch a command or

datafromthe computer's memory.

Decoding

Before a command can be executed, the control

unit must decode the command into instructionset.


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Executing

When the command is executed, the CPU carried

out the instructionsin order by converting theminto macrocode.

Storing

The CPU may be required to storethe result ofan instructionin memory.


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Most computers are digital

Recognize only two discrete states: onor off Use a binary systemto recognize two states

Use number system with two unique digits: 0 and 1, called

bits(short for binary digits)

Byte- eight (8) bits grouped together as a unit

Provides enough different combinations of 0s and 1s torepresent 256 individual characters

(numbers, uppercase and lowercase letters, punctuation

marks, and other)

Word the number of bits the CPU processes as a unit

Typically a whole number of bytes

The larger the word, the more powerful the computer

Personal computers typically 32 or 64 bits in length


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ASCII (American Standard Code for

Information Interchange) is the most widelyused coding scheme to represent data


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Electronic components that storeinstructions,data, andresults

Consists of one or more chips on

motherboard or other circuit board

Each byte stored in unique location called anaddress, similar to seats in a concert hall


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The system unit contains two types ofmemory:

Volatilememory

Loses its contentswhen power is turned

off

Example includes RAM

Nonvolatilememory

Does not lose contentswhen power is

removed

Examples include ROM,flash memory, and

CMOS


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Also known asprimary storage,primary memory,

main storage,internal storage andmain

memory.

Memory keeps the instructions and data for

whatever programs you happen to be using at

the moment.

Most RAM is volatile, it is lost when computers

power is turned off

Memory chips that can be read from and written

to by processor

The more RAM a computer has, the faster itresponds


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Dynamic RAM Must be continuously refreshed by CPU or it loses

its contents

Used for personal computer memory because of

its size and cost advantage.

Dynamic RAM is more commonly used for personal

computer memory

Static RAM Retains its contents with intervention from CPU

Faster and more expensive than DRAM

static RAM chips are preferred when energy efficiencyis a concern.

Static RAM chips are often used in cars, household

appliances and handheld electronic devices.


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Helps speed computer processes by storingfrequently used instructions and data

Also called memory cache


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Memory chips that storepermanent dataand instructions

Nonvolatile memory, it is not lost when

computers power is turned offContains programs and data permanently

recorded into memory at the factory

Cannot be changed by user

Not volatile: contents do not disappear whenpower is lost


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Nonvolatile memory that can be erased

electronically and rewritten.

Used with PDAs, smart phones, printers,

digital cameras, automotive devices,

audio players, digital voice recorders, andpagers

Nonvolatile RAM

Used in cellular phones, digital cameras, and

some handheld computers Flash memory chips resemble credit cards

Smaller than disk drive and require less power


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Complementary metal-oxide semiconductormemory

Used in some RAM chips, flash memory chips,

and other types of memory chips

Uses battery power to retain information

when other power is turned off

Stores date, time, and computers startup

information


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Expansion Slot An opening, or socket, on

the motherboard that can hold an adapter

card expansion slot

With Plug and Play, the computerautomatically can configure adapter cards

and other peripherals as you install them


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Adapter Cards Enhances system unit or provides

connections to external devices calledperipherals

Also called an expansion card


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Unlike adapter cards, you can change removableflash memory device without having to open the

system unit or restart the computer.

Removable flash memory includes memory cars, USB

flash drives, and PC Cards/ExpressCard modules.

An ExpressCard module adds memory, storage, sound,fax/modem, communications, and other capabilities

to notebook computers

A flash memory card allows users to transfer data

from mobile devices to desktop computers USB Flash drive

An PC card adds various capabilities to computers


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Port connects external devices to systemunit

Connector joins cable to peripheral

Types of ports:

1. Serial port

Transmits one bit of data at a time

Connects slow-speed devices, such as mouse,

keyboard, modem


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2. Parallel port Connects devices that can transfer more than

one bit at a time, such as a printer

3. USB ports

AUSB portcan connect up to 127 differentperipherals together with a single connector

You can attach multiple peripherals using a

single USB port with a USB hub


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4. FireWire ports

Connects multiple types of devices thatrequire faster data transmission speeds

5. Special-purpose ports

Allow users to attach specialized peripheralsor transmit data to wireless devices

MIDI (Musical Instrument Digital Interface)port, eSATA port, SCSI port, IrDA (InfraredData Association) port, Bluetooth port


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On a notebook computer, the ports are on the back,

front, and/or sides

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Channel that allows devices inside computerto communicate with each other

System bus connects processor and RAM

Bus width determines number of bits

transmitted at one time

expansion bus Allows processor to

communicate with peripherals


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Opening inside system unit used to install

additional equipment

Drive bays typically hold disk drives


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Converts AC Power into DC Power

Fan keeps system unit components cool External peripherals might use an AC

adapter, which is an external power supply

chapter 03-system unit

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