Structure of a computer

STRUCTURE OF A COMPUTER

A computer is an electronic device capable of manipulating number and symbols, first taking input, processing it, storing and giving out output under a control of set instructions which is known as a program. A general purpose computer requires the following hardware components: memory, storage device (hard disk drive), input device (keyboard, mouse etc.), output device (screen, printer etc.) and central processing unit (CPU). Many other components are involved in addition to the listed components to work together efficiently.

Computers can be classified by size and power as follows:

Personal computer: Personal computers are small computers based on a microprocessor. A personal computer has a keyboard for inputting data, a monitor for output and a storage device for saving data.

Workstation: workstations are usually powerful than a personal computer. It has more powerful microprocessor and a higher-quality monitor.

Minicomputer: Mini computers are multi-user computer capable of supporting from 10 to hundreds of users simultaneously.

Mainframe computer: Mainframe computers are powerful multi-user computer capable of supporting many hundreds or thousands of users simultaneously.

Super computer: Super computers are extremely fast computers that can perform hundreds of millions of instructions per second.

Computer organization

Computer design – an application of digital logic design procedures

Computer = processing unit + memory system

Processing unit = control + datapath

Control = finite state machine

inputs = machine instruction, datapath conditions

outputs = register transfer control signals, ALU operation codes

instruction interpretation = instruction fetch, decode, execute

Datapath = functional units + registers

functional units = ALU, multipliers, dividers, etc.

registers = program counter, shifters, storage registers

A computer consists of three main parts:

A processor (CPU)

A main-memory system

An I/O system

¾ The CPU consists of a control unit, registers, the

arithmetic and logic unit, the instruction execution unit,

and the interconnections among these components

¾ The information handled by a computer

Instruction

Govern the transfer information within a computer as well as

between the computer and its I/O devices

Specify the arithmetic and logic operations to be performed

Data

Numbers and encoded characters that are used as operands by the

Instructions

A list of instructions that performs a task is called a

program

¾ The program usually is stored in a memory called

program memory

¾ The computer is completely controlled by the stored

program, except for possible external interruption by an

operator or by I/O devices connected to the machine

¾ Information handled by a computer must be encoded in a

suitable format. Most present-day hardware employs

digital circuits that have only two stable states, 0 (OFF)

and 1 (ON)

Memory

The storage area in which programs are kept when they are

running and that contains the data needed by the running

programs

¾ Types of memory

Volatile memory: storage that retains data only if it is receiving

power, such as dynamic random access memory (DRAM)

Nonvolatile memory: a form of memory that retains data even in

the absence of a power source and that is used to store programs

between runs, such as flash memory

¾ Usually, a computer has two classes of storage

Primary memory and secondary memory

¾ Primary memory