Lecture No 4

System Unit

Central Processing Unit

RAM

What is the system unit?

A boxlike case that houses the computer’s main hardware components

What are the different types of system units?

DesktopsNotebook

Personal Digital Assistant

What’s inside the system unit?

Motherboard (mainboard)- Large circuit board with thousands of electrical circuits

Power supply- provide electric power of all parts of the system unit through main board.

Cooling fan- Keeps the system unit cool

Internal Speaker- Used for beeps when error is encountered

Drive bays- Housing for the computer’s hard drive, floppy drive and CD-ROM / DVD-ROM drives

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What’s on the motherboard?

Microprocessor (CPU)- Central processing unit interprets and carries out instructions given by software

Memory- Enables the computer to retain information

Chipset- A collection of chips that provide the switching circuitry needed to move data

Input/Output buses- Pathways that allow the microprocessor to communicate with input and output devices

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The MotherboardMicroprocessor

Keyboard / Mouse Ports

Printer Port

Video Port

PCI Slots(Peripheral Component Interconnect)

Memory Slots

AGP Slot(Accelerated Graphics Port)

Chipset

Central Processing Unit (CPU)Central Processing Unit (CPU)

The central processing unit, is the “brain” of computer system.Administrative section of computer.Supervises the operations of the other computer units.CPU is connected to all other parts of computer.Receives data and instructions given by user, processes

accordingly and produces the output.This section not only executes the instructions but also controls

all the permanent or temporary storage of data, I/O activities as well as the function of different devices attached with it.

It is further divided into two parts:◦ Control Unit (CU)◦ Arithmetic Logic Unit (ALU)

What are the types of CPUs?

IntelAdvanced Micro Devices (AMD)

CyrixMotorola (Apple)

Pentium IV

Pentium MMX

Pentium III

Basic Operation Performed by CPU (Control Unit )

Intel

4 basic operations:Fetch – The Control Unit takes the instruction that is store in the Main Memory.

Decode - The Control Unit translates the instruction into machine language or binary code.

Execute - carry out the command

Store - write the result to memory

Arithmetic and Logic Unit (ALU)Arithmetic and Logic Unit (ALU)

• Major processing unit of the CPU.• All arithmetic and logical (decision making) activities are

performed in this section.• Arithmetic means all sort of addition, subtraction, division and

multiplication.• The logical operations performed in this unit make it possible for

computer to make decisions by comparing one item with the other.

Arithmetic (addition, subtraction, multiplication, and division)

Comparison (greater than, equal to, or less than)

Arithmetic and Logic Unit

4 operations of the CPU comprise a machine cycle.

e-time

i-time

Machine Cycle

Instruction time– time to fetch and decode

Execution time– time to execute and Store

A student enters a math problem into the memory of the computer

Step 1: The control unit fetches the math problem from memory

Step 2: The control unit decodes the math problem and sends it to the ALU

Step 3: The ALU executes the math problem

Step 4: The results of the math problem are stored in memory

The result in memory displays on the screen of the monitor

Example

Control unit ALU

Memory

How a CPU worksClick to animate. Click one time only

What is memory?

A term for a device that enables the computer to retain (store) information.

What are the types of memory?

Volatile memory (Random Access Memory/RAM; Cache Memory; Virtual Memory)- Contents of memory are erased when power supply is turned off. Also called Temporary storage.

Nonvolatile memory (Read Only Memory/ROM; Flash Memory)- Contents of memory are not erased when power is turned off. Also called Permanent storage.

What is Random Access Memory / RAM?

A type of volatile memory that stores information temporarily so that it’s available to the CPU.

HOW DOES RAM WORK?

CHIPS CONTAIN MEMORY LOCATIONS CALLED MEMORY ADDRESSES

THE CPU STORES AND RETRIEVES DATA BY GOING TO THE MEMORY ADDRESSES

Intel

WEB

KEYBOARD

CPU

RAM

MONITOR

CLICK TO BEGIN ANIMATION

HOW RAM WORKS

What is cache memory?

Located within the CPU chip, it is the memory the microprocessor uses to store frequently used instructions and data.

Faster than RAM

What is virtual memory?

Part of the hard disk is reserved as RAM

When RAM modules become full the CPU accesses the hard disk to store and retrieve data

Slower than RAM

FULL

What are input/output (I/O) buses?

Pathways that enable the CPU to communicate with input/output devices

Typically the buses contain slots called expansion slots, in which expansion cards are inserted

Expansion slots

Expansion card

What’s on the outside of the system unit? Power switch- Located on the back; turns power on/off

to the computer

Receptacles- Called connectors or ports; Usually located on the back; Used to plug in peripheral devices, keyboard, mouse and monitor

Front panel- Contains drive bays, various buttons and lights

Drive bays

On/off switch

Reset button

Indicator lights

FRONTBACK

Types of ports/connectors