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					Chapter 2 – Types of Computer

Computers are classified according to their application, work, size, capacity, speed, brand, model etc.

                                                            Computers



        On the basis of                   On the basis of               On the basis of      On the basis of
            Work                               Size                         Model                Brand

             Analog                            Super                        XT                    IBM PC/ Branded

             Digital                           Mainframe                    AT                    IBM Compatible

             Hybrid                            Mini                         PS/2                  Apple/Macintosh

                                               Micro


1. Classification based on Work (or function or application)
   On the basis of the technology that is used for the functioning of the computers, they can be divided in
   three categories: digital, analog and hybrid.

     a) Analog Computer
         Analog computers work upon continuous data.
         Analog computers measure physical magnitudes such as voltage, temperature, current and
           pressure.
         E.g. Thermometer, Speedometer etc.

     b) Digital Computer
         Digital computers work upon discontinuous data.
         These computers work on binary digits 0 and 1.
         Two types of digital computers:
            Special Purpose Computer – Digital Clock, Calculator
            General Purpose Computer – PC in computer lab

     c) Hybrid Computer
         Hybrid computers are computers that comprise features of analog computers and digital
           computers.
         The digital component normally serves as the controller and provides logical operations, while the
           analog component normally serves as a solver of differential equations.
         E.g. Computers used in ICU of hospital, jet planes etc.

2. Classification based on Size
   We can classify the computers on the basis of size as below:

     a) Super Computer
         Super Computers contain several processors which work together to make it immensely powerful
           and fast.
         Used to forecast the weather and global climates, in military research and defense system.
         Used in seismography, plasma and nuclear research, in encrypting and decoding sensitive
           intelligence information.
         E.g. CRAY, NEC Super SXII, CYBER 205 etc.




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     b) Mainframe Computer
         Powerful multi-user computer used in large business organizations, examination, industries and
           defense to process complex data.
         It uses several CPU for data processing.
         More than 100 users can use at a time.
         Used in Credit card processing, Air traffic control system etc.
         E.g. IBM S/390, ICL 39 etc.

     c) Minicomputer
         Larger and more powerful than most microcomputers but are smaller and less powerful than
           mainframe computer systems.
         A multi-user computers and supports more than dozens of people at a time.
         Used in university, large business organizations to process complex data.
         E.g. PDP-11, VAX etc.

     d) Microcomputer
         Microcomputer has its CPU on one microprocessor.
         It is a single-user machine i.e. only one user can work at a time.
         Commonly used in offices, homes, schools, shops to perform different data processing jobs.
         E.g. IBM PCs, Apple Mac. etc.

3. Classification based on Model
   On the basis of model, microcomputers are classified as below:

     a) XT (Extended Technology) Computer
         It has 8086 or 8088 microprocessor.
         Its processing speed is 4.7 MHz and cannot support GUI (Graphics User Interface) based OS.

     b) AT (Advanced Technology) Computer
         It has 80286 or more advanced microprocessor and faster than XT Computers.
         It supports GUI based OS (Operating System) and applications.

     c) PS/2 (Personal System -2 ) Computer
         It uses refined architecture and faster than AT computers.
         It is a laptop computer with rechargeable and battery based system.
         It is operated with OS/2 operating system.

4. Classification based on Brand
   On the basis of brand the following three categories are available.

     a) IBM PC (International Business Machine Personal Computer)
         These computers are manufactured by IBM Company.
         IBM manufactured mainframe computers followed by mini and microcomputers.
         The microcomputer manufactured by IBM Company is called as IBM PC.
         These computers are more reliable, durable and have better quality.

     b) IBM Compatible
         It has the same functional characteristics and the principles of IBM PC.
         They are cheaper and their parts are easily available in the market.
         Most of the microcomputers used in Nepal are IBM Compatibles.

     c) Apple/Macintosh Computer
         Macintosh Computers are manufactures by Apple Company.
         The Apple Computers have their own software and hardware and are different from IBM
           computers.
         Most of the Desktop Publishing houses use Apple/Macintosh because they have high quality
           graphics.
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