Functional units of a computer

What are the main functional units of a computer? Describe the functions of each unit.

A computer can process data, pictures, sound and graphics. They can solve highly complicated problems quickly and accurately. These multidimensional functions of a computer are executed by a logical and orderly combination of some functional units described as follows:

 

 Fig: Block Diagram of Computer showing the major functional units 

 

1. Input Unit:

Computers need to receive data and instruction in order to solve any problem. Therefore we need to input the data and instructions into the computers. The input unit consists of one or more input devices. Keyboard is the one of the most commonly used input device. Other commonly used input devices are the mouse, floppy disk drive, magnetic tape, etc. All the input devices perform the following functions:

§  Accept the data and instructions from the outside world.

§  Convert it to a form that the computer can understand.

§  Supply the converted data to the computer system for further processing.

2. Processing Unit: This is the responsible for processing all the various operations that goes on in the system unit. It is referred to as the brain of the computer system, without it the computer will be valueless. Example of processing unit is the central processing unit (CPU).

The CPU is like brain performs the following functions:

§  It performs all calculations

§  It takes all decisions

§  It controls all units of the computer
 

The processing unit can be divided into three sections:

i. Memory/Storage Unit

ii. Control Unit

iii. Arithmetic and logical unit (ALU)

The Memory/Storage Unit: The storage unit of the computer holds data and instructions that are entered through the input unit, before they are processed. It preserves the intermediate and final results before these are sent to the output devices. It also saves the data for the later use. The various storage devices of a computer system are divided into two categories.

§  Primary Storage: Stores and provides very fast. This memory is generally used to hold the program being currently executed in the computer, the data being received from the input unit, the intermediate and final results of the program. The primary memory is temporary in nature. The data is lost, when the computer is switched off. In order to store the data permanently, the data has to be transferred to the secondary memory.
The cost of the primary storage is more compared to the secondary storage. Therefore most computers have limited primary storage capacity.

§  Secondary Storage: Secondary storage is used like an archive. It stores several programs, documents, data bases etc. The programs that you run on the computer are first transferred to the primary memory before it is actually run. Whenever the results are saved, again they get stored in the secondary memory. The secondary memory is slower and cheaper than the primary memory. Some of the commonly used secondary memory devices are Hard disk, CD, etc.,

The Control Unit: It controls all other units in the computer. The control unit instructs the input unit, where to store the data after receiving it from the user. It controls the flow of data and instructions from the storage unit to ALU. It also controls the flow of results from the ALU to the storage unit. The control unit is generally referred as the central nervous system of the computer that control and synchronizes its working.

Functions of the control unit:

• It carries out many tasks such as decoding, fetching, handling the execution and finally storing the results.
• It controls the execution of instructions in a sequential order.
• It guides the flow of data through the different parts of the computer.
• It interprets the instructions.
• It regulates the time controls of the processor.
• It sends and receives control signals from various peripheral devices.

The Arithmetic and Logical Unit (ALU): This unit is responsible for performing all the various Arithmetic operation of addition, subtraction, multiplication, division and relational operations Such as not equal to (≠), greater than (>), less than (< ), greater than or equal to (≥) and logical operations Etc. Whenever calculations are required, the control unit transfers the data from storage unit to ALU once the computations are done, the results are transferred to the storage unit by the control unit and then it is send to the output unit for displaying results.

Main Functions:

§  All calculations are performed in the Arithmetic Logic Unit (ALU) of the computer.

§  It also does comparison and takes decision.

3. Output Unit: The output unit of a computer provides the information and results of a computation to outside world. Printers, Visual Display Unit (VDU) are the commonly used output devices. Other commonly used output devices are floppy disk drive, hard disk drive, and magnetic tape drive.