Created By: N.AlJaffan
Modified By:S.Abudawood & Tr.Asma Aleisa
System Unit

is a case that contains electronic components of the computer used to process
data.
 Made of metal or plastic to protects the internal components from damage.
 All computers have a system unit. It is available in variety of shapes &
sizes.
The Components of the system unit

System
unit
System
unit
System unit
System
unit
System unit
Handheld controller

The Components of the system unit
1.
2.
3.
4.
5.
6.
7.

Processor interprets & carries out the basic instructions that operate a
computer.
Memory holds data waiting to be processed & instruction waiting to be
executed.
Processor & Memory are connected to a circuit board called the
motherboard.
Adapter cards (expansion slots): are circuit boards that provide
connections and functions not built into the motherboard.
Devices outside the system unit often attach to the ports.
A drive bay holds one or more disk drive.
The Power supply provide the computer with the electricity.
Motherboard

called system board.
 It is a main circuit board
of the system unit.
 Many electronic
components attach to the
motherboard, others are
built into it. Ex: adapter
cards, a processor chip
and a memory module.
http://www.howstuffworks.com/microprocessor.htm
Processor

called the central processing
unit (CPU),
Microprocessor.
 Its contain a control unit & an
arithmetic logic unit (ALU).
 These 2 components work
together to perform processing
operations.
CPU
Control
Unit
Arithmetic/
Logic Unit
(ALU)
Processor
Control
Unit
ALU
Instructions
Data
Information
INPUT
DEVICES
Data
MEMORY
Instructions
Data
Information
Storage
Devices
information
OUTPUT
DEVICES
The operations typically performed
by a CPU are

1. CPUs control the reading of programs and input files.
2. CPUs process data according to instructions in a program.
3. CPUs control the creation of output.
The Components of the system unit

The Arithmetic Logic Unit
performs arithmetic, comparison and other operations.
The Control Unit
Handles the transmission of data into and out of the
CPU and supervises its overall operations.
Registers

The CPU contain special storage areas called registers.
Their function is to hold instructions, data values, memory addresses of both
the instructions and data.
There are 4 basic types of it:
1. Instruction register hold instruction
2. Address register hold address of( data , next instruction ).
3. Storage register store data retrieved from main memory prior to
processing.
4. Accumulator store the results of arithmetic & logic operations
The System Clock

 Every CPU has a clock, It’s a small quartz crystal circuit , which
generates regular clock pulses that control the timing of all computer
operations.
 Processing actions occur at each “tick” of the electronic clock.
 The Speed of the clock determines the speed at which the CPU can
process data.
 Speed is measured in megahertz (MHz) or (GHz).
Comparison of Personal computer
Processors

The leading processor chip
manufacturers for personal
computers are
 Intel (used in PCs)
 AMD ( advanced Micro Devices)
(used in PCs)
 Motorola ( used in Apple)
 Alpha (used in workstations
and high-end servers)
How the CPU represents data

 Binary system based on two digits 0
and 1. 0 : off
1 : on
 Bit is a the smallest unit of data the
computer can process.
 Byte a group of 8 bits.
 A byte can be represent characters.
 Characters can be a letter, digit, or
symbol.
8-bit byte for the number 3
Binary Digit
(bit)
Electronic
Charge
Electronic
State
How the CPU represents data

The different combinations of 0s and 1s
are defined by patterns called a
coding schema.
There are tow popular coding scheme:
1. ASCII stands for American
Standard Code for Information
Interchange.
2. EBCDIC stand for Extended
Binary Coded Decimal
Interchange Code.
Data Representation
8-bit byte for the number 3
8-bit byte for the number 5
8-bit byte for the capital letter T

Memory

 Memory consist of electronic components that store
instructions waiting to be executed by the processor, data
needed by those instructions, and the results of
processed data ( information).
 Memory usually consist of one or more chips on the
motherboard.
Memory

Stores 3 basic categories of items:
1. The operations
2. Application programs
3. The data being processed by the application
programs and resulting information.
Memory sizes

It’s the number of bytes the chip or devices has available for
storage.
Term
Abb.
Approximate no. of
byte
Exact no. of
byte
Kilobyte
KB or K
1000
1,024
Megabyte
MB
1Million
1,048,576
Gigabyte
GB
1Billion
1,073,741, 824
Terabyte
TB
1 Trillion
1,099,511,627,776
Type of Memory

The system unit contains tow types of memory:
1. Volatile memory -
 Loses its contents .
 Temporary memory.
 Example, RAM.
2. Nonvolatile memory-
 doesn't lose its content when power is removed form
the computer.
 Permanent memory.
 Example, ROM, Flash memory, and CMOS.
RAM ( Random Access Memory ),

Also Called main memory.
 consists of memory chips that can be read from and written to
by the processor and other devices.
 The content my changed.
Saving is a process of copying items from RAM to a storage
device such as a hard disk.
Memory

RAM ( Random Access Memory )
 RAM chips usually reside on a memory module, which is a small circuit
board.
 Memory slots on the motherboard hold memory modules.
ROM ( Read Only Memory)

 The data on most ROM chips cannot be modified.
 Manufacture of ROM chips often record data,
instructions, or information on the chip when they
manufacture the chip.
 Computers almost always contain a small amount of
read-only memory that holds instructions for starting
up the computer.
Types of ROM

 PROM (programmable read-only memory): A PROM is a memory chip
on which you can store a program. But once the PROM has been used, you
cannot wipe it clean and use it to store something else. Like ROMs, PROMs are
non-volatile.
 EPROM (erasable programmable read-only memory): An EPROM is a
special type of PROM that can be erased by exposing it to ultraviolet light.
 EEPROM (electrically erasable programmable read-only memory):
An EEPROM is a special type of PROM that can be erased by exposing it to an
electrical charge.
Memory Access Time

 It is the amount of time takes the processor to read
data, instructions, information from memory.
 It’s affects how fast the computer process data.
 Access time on memory can be more than 200,000
times faster than accessing data on a hard disk
because the mechanical motion of it.
Memory

Memory Access Time
Term
Abb.
Speed
Millisecond
ms
One-thousandth of a second
Microsecond
μs
One-millionth of a second
Nanosecond
ns
One-billion of a second
Picosecond
ps
One-trillionth of a second
Expansion Slot and Adapter Cards

 Expansion slot is a socket on the motherboard that can
hold an adapter card
 Adapter card sometimes called an expansion card

is a circuit board that enhances functions of a component of the
system unit and/or provides connections to peripherals.
 Peripheral is a device that connects to a system unit and is
controlled by the processor. Ex: keyboard, printer.
Expansion Slot and Adapter Cards

Types of adapter cards
Adapter Card
Purpose
Graphics accelerator
Increases the speed at which graphics are displayed
Modem
Connect other computers through telephone or cable TV line
Network
Connects other computers and peripherals
Sound
Connects speakers or microphone
Video
Connects a monitor
Ports and Connectors

Port is the point at which a peripheral attaches to or
communicates with a system unit so the peripheral can send
data to or receive information from the computer.
 the term jack sometimes is used to identify audio and video
ports.
 Port have a different types of connectors, A connectors joins
a cable to a peripheral.
Ports and Connectors

Serial Ports is a type of interface that connects a device to the system unit by transmitting data one
bit at a time.
Ports and Connectors

Parallel Ports is an interface that connects a
device by transferring more than one bit at a
time.
 The printers using a parallel port.

Ports and Connectors

USB Ports, Short for universal
serial bus port.
 Can connect up to 127
different peripherals
together with a single
connector.
 USB hub is a device that
plugs in a USB port on the
system & contains multiple
USB ports.
Ports and Connectors

FireWire Ports Previously called an IEEE 1394 port.
 It is similar to a USB port in that it can connect multiple
type of device that require faster data transmission
speeds to a single connector, such as digital video
camera, color printers, scanners, .. etc.
 Allow you to connect up to 63 devices together.
 You can use a FireWire hub to attach multiple devices
to a single FireWire port.
 USB and FireWire are replacing all other types of port.
Ports and Connectors

Special-Purpose Ports
These ports are not included in typical computers.
 MIDI Port
 SCSI Port
 IrDA Port
 Bluetooth Port
Ports and Connectors

MIDI Port, short for musical instrument digital interface.
 Serial port
 Connect the system unit to keyboard.
SCSI Port
 A special high-speed parallel port.
 Allow you to attach SCSI peripherals such as disk driver and
printers.
Ports and Connectors

Ports and Connectors

BUSES
a set of electronic signal pathways that allows information and signals
to travel between components inside or outside of a computer.
Buses transfer bits
 from input devices to memory.
 from the processor to memory, and from memory to the processor.
 from memory to output devices.
Power Supply

Power Supply
Is a component of the system unit
that supply computer with
power.