Tuesday, March 9, 2010


A programmable machine. The two principal characteristics of a computer are:
  • It responds to a specific set of instructions in a well-defined manner.
  • Modern computers are electronic and digital. The actual machinery -- wires, transistors, and circuits -- is called hardware; the instructions and data are called software.

    All general-purpose computers require the following hardware components:

  • memory : Enables a computer to store, at least temporarily, data and programs.
  • mass storage device : Allows a computer to permanently retain large amounts of data. Common mass storage devices include disk drives and tape drives.
  • input device : Usually a keyboard and mouse, the input device is the conduit through which data and instructions enter a computer.
  • output device : A display screen, printer, or other device that lets you see what the computer has accomplished.
  • central processing unit (CPU): The heart of the computer, this is the component that actually executes instructions.
  • In addition to these components, many others make it possible for the basic components to work together efficiently. For example, every computer requires a bus that transmits data from one part of the computer to another.

    Computers can be generally classified by size and power as follows, though there is considerable overlap:

  • personal computer : A small, single-user computer based on a microprocessor. In addition to the microprocessor, a personal computer has a keyboard for entering data, a monitor for displaying information, and a storage device for saving data.
  • workstation : A powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and a higher-quality monitor.
  • minicomputer : A multi-user computer capable of supporting from 10 to hundreds of users simultaneously.
  • mainframe : A powerful multi-user computer capable of supporting many hundreds or thousands of users simultaneously.
  • supercomputer : An extremely fast computer that can perform hundreds of millions of instructions per second.
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