The Components of the system unit
Created By: N.AlJaffan
Modified By:S.Abudawood
The Components of the system unit
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
The Components of the system unit
1. Processor interprets & carries out the basic instructions that
operate a computer.
2. Memory holds data waiting to be processed & instruction waiting
to be executed.
3. Processor & Memory are connected to a circuit board called the
motherboard.
4. Adapter cards (expansion slots): are circuit boards that
provide connections and functions not built into the motherboard.
5. Devices outside the system unit often attach to the ports.
6. A drive bay holds one or more disk drive.
7. The Power supply provide the computer with the electricity.
The Components of the system unit
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
Central Processing Unit (CPU)
Processor, called the central processing unit (CPU), Microprocessor.
CPU
Control Unit
Arithmetic/
Logic Unit
(ALU)
Its contain a control unit & an arithmetic logic unit (ALU).
These 2 components work together to perform processing
operations.
Processor
Control
Unit
ALU
Instructions
Data
Information
INPUT
DEVICES
Data
MEMORY
Instructions
Data
Information
Storage
Devices
information
OUTPUT
DEVICES
Central Processing Unit (CPU)
The operations typically performed by a CPU are:
1.
2.
3.
CPUs control the reading of programs and input files.
CPUs process data according to instructions in a program.
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.
Central Processing Unit (CPU)
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
Central Processing Unit (CPU)
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).
Central Processing Unit (CPU)
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)
Central Processing Unit (CPU)
How the CPU represents data
 Binary system based on two digits 0 and 1.
Binary
Digit (bit)




Electronic
Charge
Electronic
State
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
Central Processing Unit (CPU)
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
 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
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
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
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 (Main Memory)
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.
RAM
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
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
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
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 Access Time Units
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 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
Graphics accelerator
Modem
Network
Sound
Video
Purpose
Increases the speed at which graphics are displayed
Connect other computers through telephone or cable TV line
Connects other computers and peripherals
Connects speakers or microphone
Connects a monitor
Ports and Connectors
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.