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 attachments
1) 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 computer
The arithmetic logic unit- performs
comparisons, arithmetic, and logic operations
Machine cycle- the repeated 4 steps to all
computer actions (1-fetching, 2-decoding, 3executing, 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 Representation
Computers use digital representation

Binary code
1=on
 0=off

A single digit is a bit
8 bits equal a byte
Two coding systems
ASCII
 EBCDIC

Memory
RAM (Random access memory)
Primary memory type
 Read from and written by programs
 If power loss RAM is lost, unless stored



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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.



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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 connectors
Serial 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 ports
Firewire 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
Buses
Buses



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

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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
Bays
Opening 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.