Basic computer organization

All computer system perform the following five basic operations:-

1. Inputting – The process of entering data and instruction into the computer system.
2. Storing – Saving data and instruction so that they are available for initial or for additional processing as and when required.
3. Processing – performing arithmetic operations. (comparisons like equal to less than, greater than, etc.) on data in order to convert them into useful information.
4. Outputting – The process of producing useful information or results for the user, such as a printed report or visual display.
5. Controlling – Directing the manner and sequence in which and all of the above operations are perfomed.

Input unit

In short the following functions are performed by an input unit:

1. It accepts (or reads) the list of instructions and data from the outside world.
2. It converts these instruction and data in computer acceptable from.
3. It supplies the converted instructions and data to the computer system for further processing.

Output unit

In short, the following functions are performed by an output unit:

1. It accepts the results produced by the computer which are in coded form and hence cannot be easily understood by us.
2. It converts these coded results to human acceptable (readable) form.
3. It supplies the converted system for further processing.

Storage unit

In short, the specific functions of the storage unit are to hold (store).

1. All the data to be processed and the instruction required for processing (received from input devices).
2. Intermediate results of processing.
3. Final result of processing before these results is released to an output device. 

Arithmetic logic unit

The arithmetic logic unit (ALU) of a computer system is the place where the actual execution of the instruction takes be more precise, all calculations are performed and all comparisons (decision) are made in the ALU.

ALU’s are designed the four basic arithmetic operations add, subtract, multiply, divide and logic operations or comparisons such as less than, equal to or greater than.

Control unit

The control unit is able to maintain order and direct the operations of the entire system it obtain instruction from the program stored in main memory interprets the instructions, and issues signals that cause other units of the system to execute them.

Control processing unit

The control unit and the arithmetic logic unit of a computer system are jointly known as the central processing unit (CPU). The CPU is the brain of any computer system. In a human body, all major decisions are taken by the brain and the other parts of the body functions as directed by the brain. Similarly in a computer system all major calculations and comparisons are made inside the CPU and the CPU is also responsible for activating and controlling the operations of other units of a computer system.