The size, shape, cost, and performance of computers have changed over the years, but the basic logical structure has not. Any computer system essentially consists of three important parts, namely, the input device, central processing unit (CPU) and output device. The CPU itself consists of the main memory, the arithmetic logic unit, and the control unit.

In addition to the three basic parts mentioned above, computers also employ secondary storage devices (also referred to as auxiliary storage or backing storage), which are used for storing data and instructions on a long-term basis.

Any computer system can perform the following five basic tasks:

    1.  Inputting: The process when the user feeds in the set of commands or instructions to process data into computer system.
    2. Storing: The process of recording data and information so that it can be retrieved for use whenever required
    3. Processing: Performing arithmetic or logical operations on data to convert them into useful information. Arithmetic operations include addition, subtraction, multiplication and division, and logical operations includes include comparisons such as equal to, less than and greater than, etc.
    4. Outputting: This is the process of providing results to the user. These can be in the form of visual display and/or printed reports.
    5. Controlling: This refers to directing the sequence and the manner in which all these previous tasks are carried out. 

Let us now familiarize ourselves with the various computer units that perform these functions.

 Input Unit

Programs and data need to be in a computer system before any kind of operation can be done. Program refers to the set of instructions which the computer has to carry out, and data is the information on which these instructions are to operate, If the task is to rearrange a list of telephone subscribers in alphabetical order, the sequence of instructions that will guide the computer through this operation is the program, while the list of names to be sorted is the data.

Component of Computer

The process of transferring data and instructions from the external environment into the computer system is performed by the Input Unit. Instructions and data enter the input unit through the particular input device used (keyboard, scanner, card reader, etc.). These instructions and data are then converted into binary codes )computer-acceptable form) and sent to the computer system for further processing.

Central Processing Unit

The central processing unit functions like the brain of the computer system, It is the combination of the control unit, the ALU, and the primary memory.

Main Memory (Primary Storage): The main memory or the primary storage of the computer system stores all the instructions and data. These are then further transferred to the Arithmetic Logical Unit (ALU) for processing and then the final output is again stored back in the primary storage until it is further sent to the output device.

The primary storage also temporarily stores any intermediate result generated by the ALU. So data and instructions shuffle frequently between the ALU and the primary storage before the processing is complete. It may be worth remembering that no processing takes place within the primary storage.

Arithmetic Logic Unit: ALUs are not only capable of performing the basic four arithmetic operations, i.e. addition, subtraction, multiplication, and division but can also perform logic comparison operations, such as equal to lesser than or greater than.

Control Unit: The function of the control unit is to ensure that according to the stored instructions, the write operation is done on the right data at the right time. The control unit receives instructions and commands from the programs in the primary memory, processes them and ensures that the commands are executed in the desired order by all the other units of the computer system. In effect, the control unit is comparable to the central nervous system of the human body.

Output Unit

Computers understand, process data and return the output in binary form. The basic function of the output unit, therefore, is to convert these results into a human-readable form before providing the output through various output devices like terminals and printers.

Secondary Storage

The storage capacity of the primary memory of the computer is limited. Often, it is necessary to store large amounts of data. So, additional memory, called secondary storage or auxiliary memory is used in used in most computer systems.

Secondary storage is storage other than the primary storage. These are peripheral devices connected to and controlled by the computer to enable permanent storage of data and programs. Typically, hardware devices like magnetic tapes and magnetic disks fall in this category.

Bhupen Sahu

Bhupen Sahu is the chief SEO expert and founder of “” He has a very deep interest in all technology topics whatsoever. His passion, dedication and quick decision making ability make him stand apart from others.


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