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Computer System – Architecture

Computer System

A computer system consists of HARDWARE (physical

machinery) SOFTWARE

(applications, programs)

Computer

A computer consists of: Input/Output devices CPU (Central Processing

Unit)/System Unit Memory Secondary storage

A Computer

MemoryMemory

Secondary StorageSecondary Storage

Input/OutputInput/Output System Unit

System Unit

Computer Types

Computer types range from small personal computers to large supercomputers.

In between are the categories of servers, minicomputers and mainframe computers.

Personal Computers (PCs)

Relatively small Inexpensive Designed for single users Desktops, laptops, notebooks,

palmtop Becoming increasingly powerful Very popular

Personal Computers (PCs)

Embedded computers or processors that are placed

inside other objects cars stereos household appliances (video, ovens etc) video systems

Servers

Computers that are designed to support a network.

Powerful CPU Capable of using more than one

CPU Large memory Large storage capacity High speed communications

Minicomputers

Computer systems that can accommodate several users at the same time.

Large storage capacity. Excellent processing

capabilities. Used in small business

Mainframes

Large, powerful and fast. Can accommodate a

large number of users at one time.

Requires separate room. Used by larger

companies and organisations.

Supercomputers

The most powerful and fastest.

Very expensive. Used for complex

calculations, military applications, simulations and high tech businesses.

The System Unit

This is where program instructions are executed and data is manipulated

Components motherboard memory co-processors microprocessor and CPU

buses expansion slots ports

Motherboard

The main board that contains the electronic components of the system unit.

Microprocessor & CPU

On a PC the CPU is contained on a single circuit called a microprocessor.

An integrated circuit is also called a chip, that is etched on a small slice of silicon.

CPU Components

Control Unit (the brain) co-ordinates the control of data and

repeats the machine cycle

FETCH

DECODE

EXECUTE

STORE

Arithmetic Logic Unit (ALU) performs arithmetic & logic operations

Registers temporary storage locations for data

immediately before, during and after execution by the CPU

CPU Components

CPU Characteristics

Speed• Clock speed (an electronic impulse)

affects the machine cycle• Measured in megahertz (MHz)

Machine Cycle• The time taken is a fraction of a second• MIPS (millions of instructions per

second) are used to measure machine cycle time

Memory

Read Only Memory (ROM) Random Access Memory

(RAM) Located close to the CPU Working storage area for

system and program instructions and data.

Fast access

Co-processors

A form of multiprocessing more than one processing unit

This speeds processing by executing specific types of instructions while the CPU processes others.

Examples of co-processors include maths and graphic processors.

Buses

Buses are the physical wiring that connects other system components.

Data is transferred along these buses

The number of bits a bus line can transfer at any one time is called the bus width 32 and 64 are common bus widths

Expansion Slots

A socket that is used to connect a circuit board to a device sound card, network card

The socket that holds the card is connected to a bus that is connected to the CPU.

Ports

A socket that is used to connect a peripheral device (printer, scanner etc) to the system unit.

Parallel Port• Used when large

amounts of data are sent or received.

• Printers, disk drives

Serial Port•Transmits one bit at a time•Much slower than parallel•Mouse, keyboard