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Computer Architecture & Organization/BASIC STRUCTURES OF COMPUTERS

Functional Units

Computers consists of 5 functionally independent parts: 1)	Input 2)	Memory 3)	ALU 4)	Output 5)	Control Unit

The input unit can get the information from outside source over digital communication line.The information received is either stored in the computer’s memory for later reference or is immediately used by the ALU to perform the desired operation.The processing steps are determined by the program stored in the memory.The results are then sent back to the outside world by the output device.All these actions are co-ordinated & controlled by the control unit.

Input Unit

Computers accept information through input units which read the data.Most well-known input device is the Keyboard.Whenever a key is pressed the corresponding character is automatically translated to the corresponding binary code & transmitted over the cable to either memory or processor.Other input devices are joysticks, trackballs & mouses.

Memory Unit

Its function is to store data & programs. There are two classes of storage: 1)	Primary 2)	Secondary

Primary StorageItalic text

It is a fast memory.This memory consists of semiconductor storage cells each capable of storing 1 bit of information. Memory in which any location can be reached in a short & fixed amount of time after specifying its address is called Random Access Memory (RAM).The time required to access one word is called Memory Access Time.The small, fast units of RAM are called Cache.

Secondary StorageItalic text

It is cheaper than primary.It is used when large amount of data & many programs have to be stored. Examples are magnetic disks, tapes, optical disks etc.

ALU

Most computer operations are executed in ALU. For e.g. suppose two nos. located at different memory locations are to be added. They are brought to the processor & the actual addition is carried out by ALU. The result is either stored in memory or frequently used by processor.

Output Unit

Its function is to send the processed results to the outside world. Examples are monitor, printers etc.

Control Unit

Its function is to coordinate the input, output, ALU & memory units. It sends the timing signal to coordinate & control the operation. Timing signals are signals that determine when a given action is to take place. A large number of control lines carry the signals used for timing are attached with the functional units.