INFORMATION TECHNOLOGY

IT is the term used to describe technologies which enable the users to record, store, process, retrieve, transmit and receive information.

WHAT IS A COMPUTER ?

A physical device that takes data as input, transforms these data according to stored instructions and output the processed information

BASIC ANATOMY OF COMPUTER

INPUT

UNIT

OUTPUT

UNIT

SECONDARY

MEMORY

MAIN

MEMORY

ALU CONTROL

UNIT

• Central Processing Unit (CPU) – It manipulates raw data into a more useful form and controls other parts of the computer system. It is referred as the “brain” of the computer system. CPU has three main parts:

– Memory Unit–Control Unit–Arithmetic Logic Unit (ALU)

• Control Unit – Obtains instructions from the computer systems’ memory, interprets them and notifies the other components in the system to carry them out.

• Control unit has special storage locations called registers.

• Main registers of control unit: – Instruction register- holds instruction currently being

executed.– Instruction address register- holds the address of the next

instruction to be executed.– General purpose register-hold data for temporary storage.– Storage address register and storage data register- hold

the address & content respectively of a storage instruction prior to data being placed into a location transferred from it.

• Arithmetic and Logic Unit (ALU) – It processes data obtained from memory under the direction of the control unit. It performs the computers’ principal logical and arithmetic operations.

• Main registers of ALU:– Accumulator- used when the unit is performing arithmetic

operations.– Program counter- keeps track of the items of information

stored in the memory cell.

• Memory Unit – The place where computer programs and data are stored during processing.

• Divided in to storage locations called bytes.• It has the following characteristics:

– Volatile– Randomly accessed– Fast– Expensive

• Main memory has three functions:-

– it stores all or part of the software program that is being executed.

– it also stores the operating system program that manage the operation of the computer.

– it holds data that the program is using.

• Random access Memory – it consists of storage locations in which data can be stored and retrieved directly.

• Read Only Memory (ROM) : which can only be read, is non-volatile,can not be written to or altered, can be changed by removing old ROM chips & inserting new ROM chips containing new programs.

• Types of ROM:

PROM (Programmable Read Only Memory)-allows to read a program into it.

EPROM (Erasable Programmable Read Only Memory)-allows programs in ROM to be altered with special equipment.

• Input unit – gather data & convert them in to electronic form. Example:---Keyboard, Terminals, Touch Screen, Joy Stick, Light Pen, Digitiser.

• Output unit- display data after they have been processed. Example:---Display Screen, Printers, Plotters.

• Secondary storage-used for long term storage of data outside the CPU. It is non-volatile. Magnetic disks,optical disk,magnetic tape are few secondary storage devices.