Lisa Schulke

The Components of the System UnitChapter 4

What exactly is the System Unit?

• A case that contains electronic components used to process data

• Sometimes called the chassis which protects the internal electronic components– Includes the Motherboard which is

the main circuit board of the system unit

More about the Motherboard

• Many electronic components attach to the board

• Those components include: adapter cards, the processor, and memory chips– A computer chip is a small piece of

semi conducting material which have integrated circuits

• Other components are built into the board

The ProcessorA component

• central processing unit• Interprets & carries

out basic instructions that operate a computer

• Manages the computer’s operations

• Contain 2 smaller components – Control unit– Arithmetic logic unit

The Control Unit The Arithmetic Logic Unit

• Directs & coordinates operation

• Interprets each instruction issued by a program & initiates the appropriate action to carry out the instruction

• Arithmetic operations– Basic calculations

• Comparison operations– Comparing 1 data

to another• Logical operations

– And, or, and Not

The Machine Cycle: 4 basic operations of a processor

1. Fetching- obtaining a program instruction or data from the memory

2. Decoding- translating instructions into signals

3. Execute- carries out the commands4. Storing- writing result to memory

Plenty more about processors

• Contains:– A register which is storage location

that temporarily holds data and instructions

– A system clock that control the timing of computer operations•Clock speed

Names of Processors

• Pentium- used by high performance PCs• Celeron- used by less expensive basic

PCs• Xeon and Itanium- ideal for workstations

and low-end servers

Processor Installation and Upgrades

• 3 types of Upgrades– Chip-for-chip– Piggyback – Daughterboard

New chips cause heat

• A heat sink is a small ceramic component that absorbs and ventilates heat produced by electrical components

• A heat pipe cools processors in notebook computers

Coprocessors and Parallel Processing

• A coprocessor is a special chip or circuit board that assists the processor in performing tasks– Floating point has

numeric capabilities

• Parallel processing is a method that uses multiple processors to execute a program.

Data Representation

• Computers communicate digitally and recognize only 2 discrete states: on and off– recognizes the 2 states by the binary

system which only has 2 unique digits( 0 & 1), called bits•8 bits form a byte

Coding scheme

• The combinations of 0s and 1s that represent characters are defined by patterns called the coding scheme– Example: #3 is represented by

00110101• The 2 popular coding schemes:

– ASCII and EBCDIC

Memory• Consists of electronic

components that store instructions waiting to be executed by the processor, data, and the results of processed data (info)

What memory stores?• 3 basic categories of items:

– The operating system and other system software that control or maintain the computer and its devices

– The application programs that carry out a specific task, such as word processing

– The data being processed by the application programs and resulting information

More about Memory

• A byte resides temporarily in a location called the address– An address is a unique number that

identifies the location of the byte

• To access data in memory, the computer references the addresses that contain bytes of data

Sizes of Memory• A kilobyte is equal to exactly 1,024 bytes• A megabyte is equal to almost 1 million

bytes• A gigabyte equals almost 1 billion bytes

2 types of Memory1. Volatile- when the computer’s power is

turned off it loses its contents2. Nonvolatile- does not lose its contents

Ram

• Stands for Random access memory or main memory

• Consists of memory chips that can be read from and written to by the processor

• It can hold multiple programs simultaneously

• Most Ram is volatile

2 basic types of ram chips

• Dynamic Ram– Must be re-

energized constantly or they lose their contents

• Static Ram– Do not have to

be re-energized as often

– More expensive– Faster and

more reliable

Where do RAM chips live?

• Usually reside on a memory module which is a small circuit board– Memory slots on the motherboard

hold memory modules• 3 types of modules:

– SIMMS (single inline memory module)– DIMMS (dual inline memory module)– RIMMS

Ram Configurations

• The amount of RAM necessary in a computer often depends on the types of software you plan to use

• The more RAM a computer has, the faster it

• A software package will indicate the minimum amount of RAM it requires

Cache: speeds up process

• Memory cache helps speed the processes of the computer because it stores used instructions and data– L1 cache has the smallest capacity– L2 cache has a larger capacity than L1– L3 cache exists only with L2 advanced

transfer cache• Disk cache

Read-only memory

• ROM refers to memory chips storing permanent data

• Data can’t be modified• ROM is nonvolatile• Rom chips are called firmware which

contain permanently written data/info• A PROM (programmable) chip is a blank

ROM which a programmer can write

Flash Memory

• A type of nonvolatile memory• Can be erased electronically and

reprogrammed• Useful for updates• Flash memory cards store flash memory

on a removable device instead of a chip

An aide to chips

• Complementary metal-oxide semiconductor (CMOS)– Technology that provides high speeds– Consumes little power– Uses battery power to retain info

Memory Access Times

• Access time is the time it takes the processor to read data/info– Directly effects how fast the computer

runs– Nanoseconds and MHz are used to

state access times– Accessing data from memory is faster

than from hard disk

Expansion slots and adapter cards

• The slot is a socket that holds adapter card• An adapter card is a circuit board

(expansion card)– Enhances functions– Provides connections to peripherals

•A peripheral connects to the system unit and is controlled by the processor

–Examples: modems, printers, scanners

Neat cards

• A sound card enhances sound by allowing sound to be input thru a microphone and output thru speakers

• A video card converts output info into a signal which displays an image on the screen

• A modem card allows computer to communicate via telephone lines, cable, etc..

• A network card allows computer to access a network

Pc cards and Flash memory cards

• A PC Card slot is an expansion slot that holds PC cards– A PC card adds memory, storage, sound,

fax/modem & communications– PC cards are 1 type of flash memory card

•A flash memory card allows users to transfer data from mobile devices to desktop computers

Ports and Connectors• The point where the

peripheral connects to the system unit

• Send data• The term jack is used

to identify audio/video ports

• Personal computers have ports in front

• Others have in back

• Joins a cable to a peripheral

• 2 genders of cables:– Male- 1+ exposed pins– Female-have matching

holes to accept the pins

• Same gender can’t connect

• Gender changer- join same gender connectors

Serial Ports

• Interface that connects a device to the system by transferring bit by bit

• Connect devices that don’t require fast data

• Examples: mouse, keyboard• The COM port is a type of serial port

Parallel Ports

• Interface that connects devices by transferring more than 1 bit at a time

• Printers are connected by this port• Also called a Centronics interface

USB Ports• Short for Universal serial bus port• Can connect up to 127 different peripherals• Uses only 1 single connector type• To attach multiple peripherals use Daisy

chain– The 1st USB device to the USB port on the

computer, then the 2nd connects to 1st and so on

• USB hub- plugs into USB port and contains multiple USB ports

Special-Purpose Ports

• Firewire- connect devices that require faster speeds

• Midi- connects the system unit to a musical instrument

• SCSI (small computer system interface)- connects disk drives and printers

• IrDa- transmits data via infrared light waves• Bluetooth- transmits data using radio

waves

Buses• Electrical channels that bits transfer on• Allows inside and outside devices to

communicate with each other• Consists of 2 parts:

– A data bus transfers actual data– An address bus transfers info where

the data is• Bus width- the # of bits the computer

can transmit at 1 time

Word Size and buses

• The number of bits the processor can interpret and execute at a give time

• Every bus has a clock speed (hertz)• 2 basic types of buses:

– A system bus connects to main memory

– An expansion bus connects to peripherals

Expansion Bus• Communicates with peripherals attached to

adapter card• Types:

– ISA (Industrial Standard Architecture)-most common

– Local- a high speed expansion that connects higher speed devices

– AGP (Accelerated Graphics Port)- designed to improve the speed with 3-D graphics

– FireWire- eliminate the need to install cards• The expansion bus for a PC Card is the PC Card

bus

Power Supply

• Converts the wall outlet AC power into DC power

• Near the supply is a fan to keep unit cool

• Some external peripherals have an AC adapter, which is an external power supply

Putting it all together

• Many components of the system unit influence the speed and power of the computer

• These include:– Type of processor– Clock speed of the processor– The amount of RAM– Clock speed of the bus

Chapter Summary

• Components of the system unit• Described how memory stores data/info• Discussed sequence of operations that

occur when a computer executes an instruction