The Components of the System Unit

Jeremy Lukianovich

The system unit

The system unit is the case that contains the electronic components that make up a computer.

The mother board is the main circuit board that all of the electronic components are in some way connected to.

Computer Chip

The computer chip is a small piece of etched semi-conducting materiel, such as silicone.

There are two types of attachments1) DIP-dual inline package (two

rows of metal feet)2) PGA-Pin grid array (large number

of pins covering the surface of the chip)

Processor-(CPU)The Control unit- directs and coordinates activities in the computerThe arithmetic logic unit- performs comparisons, arithmetic, and logic operationsMachine cycle- the repeated 4 steps to all computer actions (1-fetching, 2-decoding, 3-executing, 4-storing)Registers-Small storage locations in the processor. This is a high speed temporary storage area.The system clock- controls timing of all computer operations

Processor installation and upgrades Three types

Chip for Chip-Replace existing chip Piggy back-stack new one on top of old chip Daughterboard upgrade-new chip on adapter card that

plugs into motherboard

Heat sinks and heat pipes ceramic or metal finned components that help dissipate

heat

Coprocessors a secondary chip that aids the main processor, thereby

increasing the performance of the computer

Parallel processing Using multiple computer processors to increase the

speed of the processor.

Data RepresentationComputers use digital representationBinary code

1=on0=off

A single digit is a bit

8 bits equal a byte

Two coding systemsASCIIEBCDIC

MemoryRAM (Random access memory)

Primary memory typeRead from and written by programs If power loss RAM is lost, unless stored

DRAM (Dynamic RAM) Must be reenergized or will lose memory Several types

SRAM (Static RAM) Most stable but expensive

More RAM the faster the computer will be

Cache Memory Cache

Stores frequently used data - speeds up computer 3 types

L1-built into processor L2-advanced transfer cache L3-separate cache, must have L2 to work

Disk Cache (see chapter 7)

ROM (Read only memory) Stores permanent data and instructions

Flash memory Nonvolatile memory that can be erased electronically Often contains startup instructions due to its adaptability

CMOS (Complimentary metal-oxide semiconductor) Technologically advanced materiel that produces high speeds with low

power draws.

Memory access times The time it takes a computer to do an operation, this can be as little as

10 nano-seconds

Expansion Slots and Adapter cards

Expansion slots Slot on computer that can hold a circuit board that in some

way increases the performance of the computer. Sound cards Video cards Modem cards Network cards

PC cards and Flash memory cards PC cards-a thin device that plugs into a computer and adds

memory, storage, sounds, modem, communications, fax, or other abilities to the computer.

Flash memory cards-a card that allows a user to add data from a mobile device (such as a PDA) to a laptop.

Ports and connectorsSerial ports-a port that connects two devices and transmits 1 bite at a time, good for devices that do no require high transfer rates.

Mouse Keyboard Modem

Parallel ports-a port connects devices but transmits data at a higher rate than a serial port

Printers

USB ports-universal serial bus port Can connect up to 127 peripherals together on one port.

Daisy chain them USB hub Hot plugging (plugging in a device without first shutting the

computer down.

Special purpose portsFirewire port

Similar to USB Faster than USB

MIDI port (musical instrument digital interface) Used to connect a instrument to a computer

SCSI (small computer system interface Attach such devices as disk drives and printers Daisy chain up to 7 to 15 devices

IrDA (infrared data ssociation) Transfer data via infrared light waves, completely

wireless

Bluetooth Radio waves to transmit information Similar to IrDA but you don’t need to line up the

devies

BusesBuses

The channels within a computer chip which the bits take to travel from one point to another.

Bus width dictates how many bits a computer may transmit and one time

Faster the bus speed the faster the programs will run.

System Buses Part of the mother board Connects processor to main memory

Expansion buses Channels outside the main processor that transmit data into and

out of the processor ISA (industry standard bus)-slowest Local- high speed bus that connects things such as disk drives Accelerated Graphics port-improves speed which 3D graphics move USB and Firewire PC Card bus

BaysOpening in system where you can insert additional equipment

Drive bays- rectangular openings which usually house disk or CD drives.

Power Supplies

Battery powered-primarily laptops

AC adaptor-allows the DC powered computer to be plugged into a AC power supply (wall socket)

A cooling fan is generally mounted near the power input

Mobile Computers and Devices

Laptops-small computers that have folding screens, very portable Contain many miniaturized components which generally raises the

price

Tablet PC-entire computer in the shape of a tablet.

PDA-handheld computing device, generally contain a phone book, basic word processing, and little else.