Classification of computers based on memory size

In terms of capacity, price performance, computers can be broadly classified as follows.

  • Main Frame Computers.
  • Mini Computers.
  • Micro Computers.

    • Main Frame Computers:
    They are most expensive of all the computers, are very big in size and offer maximum computing power. A large number of peripherals can be attached to them. They are generally used in large networks and the mainframe works as central computer or node. All other smaller terminals are connected to central computer or server through satellite link.
    A typical example is the air line reservation system. The main frame computer is placed at the head office, where all the information about all flights is stored and small computers are placed at various branches and are attached to the central data bank so that up to date information of all flights is always available.
    The structural configuration of mainframe consists of

  • Data communication equipment.
  • Interface equipment.
  • Primary storage.
  • Secondary storage.
  • Central processors with multiprogramming facilities.

    • Characteristics:

  • These are large general purpose computers capable of handling all kinds of problems whether scientific or commercial.
  • Can accept and transfer data from I/O devices at the rate of million bytes per second.
  • Can accept all type of high level languages.
  • Can support large number of terminals say up to 100 or more?
  • They have flexibility to operate automatically.
  • They have high on line secondary storage capacity and can support a number of peripheral devices like magnetic tape drives, hard disk drives, visual display units etc.
  • They have high cache memory, to process applications faster than mini or micro computers.

    • Mini Computers:
    These are the smaller versions of the mainframe. They offer same computing power as their bigger counterparts but a small/number of peripherals can be attached to the mini computer. It is comparatively cheaper in cost, small in size, very rugged and reliable. It does not require air conditioning and can be operated at room temperature. In business environment a mini system can be ‘tailor made’ for job specification.

    Characteristics:

  • They can accept and transfer data from I/O devices at the maximum speed of 4 million bytes per second.
  • Can support up to a maximum of 20 terminals.
  • They usually employ microprocessors in the CPU for data storage and data manipulation.
  • They have faster processing speed.
  • In most mini computers, data and instructions are stored in fixed word locations.
    They have main memory ranging from 256kb to 12 Mb and word length of 16/32 bits and are designed for 4 to 8 users in time sharing models.

    • Mini Computers can be sub classified in to

  • Mini minis
  • Midi minis
  • Maxi minis(super minis)

    • Micro Computers (also termed as miniaturized mini computer):
    They can carry input, storage, arithmetic, logic, control and output functions.
    They use silicon made micro processor chips which are of a size of 5mm square and 0.1 mm thick, with layers of etched and printed circuits-containing all elements required to process binary encoded data.
    These systems use random access memory and read only memory as primary storage.
    They range from single board size to a system containing many circuit boards mounted in a cabinet. They are light enough to be moved easily and are designed to be used by one person at a time.
    A typical microcomputer has a keyboard for input and user diskettes and floppy disk drives to enter data and programs and to receive processed outputs. They use magnetic tape and floppy discs as secondary storage devices.
    A visual display unit and/or character printer is used to prepare output in a human readable form. All micro computers are byte addressable machines. They use micro processor chips viz.

    Features of Micro Computers:
    They use very little power, require little air conditioning and does not require special wiring, raised floors.
    They are stable and reliable.

    Personal Computers:
    They are the one of the latest type of micro computers. They are called so because they are designed for personal use of individuals or small business units, office automation units or professionals.
    Personal computers can be used for basic programming, fun and games, business and professional applications, tele communications; data base management, accounting, and word processing.