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    Computers can be classified based on the following criteria

    1. Development of technology (by generation)
    2. Principle of operation (by type)
    3. Storage capacity or by configuration (by size)
    4. Degree of versatility (by purpose)


    Classification by types

    Computers can be classified into three major types based on principles of operations.

    The three types are

    1. Digital computer
    2. Analog computer
    3. Hybrid computer


    i) Digital Computer: These are computer that perform calculation and logical operations with quantities represented as digits in binary number system. They operate on digital data such as numbers which are referred to discrete values. Digital computers give more accurate and faster results. They are counting devices. Examples are digital clocks, mobile phones, calculations, microcomputers, etc.


    ii) Analog Computers: These are computers that work on continuous values. It operates by measuring rather than counting. It uses continuous signals as input. It generally deals with physical variables such as voltage, pressure, temperature, speed, etc. it is not as accurate as digital computers. Examples of analog computers are speedometer, scale machine, barometer, thermometer, etc.


    iii) Hybrid Computer: These combine the features of digital and analog computers. They are mostly used for automatic operations of complicated process and machine. There are also used with process control equipment in continuous production of plants in refineries as well as places where signals and data are to be entered into the computer.

    Areas of application of hybrid computers are unclear power plants, mines, Intensive Care Unit (ICUs), chemical processing plants, etc.


    Classification of computers by sizes

    Based on size and storage capacity, computers can be divided into four which are.

    1. Micro computer
    2. Mini computer
    3. Mainframe computer
    4. Super computer


    i) Micro computers: These are small, low cost and single-user digital computers. They consist of a CPU, input unit, output unit, storage unit and the software. Micro computers are often called Personal Computer (PCs). They can be further classified into desktop computers, notebooks, tablet computers, smartphones, handheld or palmtop computers.

    Examples of micro computers are IBM PC based on Pentium micro processor and Apple Macintosh.


    ii) Mini Computer: These are digital computers generally used in multi-user systems. They are medium sized computers much larger than PCs but smaller than mainframe computers. They have high processing speed and high storage capacity than the micro computers. They can support 4 – 200 users simultaneously. The users can access the mini computer through their PCs or terminals.

    Mini computers are mainly used as small or mid-range servers operating business and scientific application. Examples of mini computers are digital Alpha, Sun ultra.


    iii) Mainframe Computers: These are multi-user, multi-programming and high performance computers. They operate at a very fast speed; they have very large storage capacity and can handle the workload of many users.

    They can support hundreds of users. They are large and powerful system generally used in centralized databases. There are also used in organizations like banks or companies where many people require frequent access to the save data. Examples are IBM 370, S/390, etc.


    iv) Super Computers: These are fastest, most expensive, largest computers with very high processing power. The speed of a super computer is generally measured in FLOPS (Floating Point Operation Per Second). Some of the fastest super computers can perform trillions of calculations per second.


    They are used for highly intensive tasks such as weather forecasting, climate research, molecular research, biological research, nuclear research, aircraft design, petroleum exploration and production, animated graphic, etc.


    They are also used in major universities, military agencies, scientific research laboratories, etc. some examples of super computers are CRAY 3, NEC-500, PRRAM 9000, ANURAG, IBM road runner, PA RAM 1000, etc.


    The difference between a super computer and a mainframe computer is that a super computer channels all its power into executing a few program as fast as possible while a mainframe uses its power to execute many programs concurrently.


    Classification of computer based on purpose

    There are two classes of computers based on purpose or functionality. They are:

    • General-Purpose Computers
    • Special Purpose Computers

    1) General-purpose Computers: These are computers that a specially designed for a particular job or task. The set of instructions required for the specific task is permanently stored in the computers memory.

    2) Special purpose computers can be found in Air traffic control, weapons guarding system, word processor machine and space research control, etc.


    See also






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