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A computer is a device that processes data according to a set of instructions called a program. Most modern computers are electronic and digital. The machinery of computers, such as the circuitry and wires, is known as hardware; the instructions and data are called software.

All general-purpose computers have 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 CD-ROMs
  • 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
Expert predictions that went wrong
    – Thomas Watson, chairman of IBM (1943)

    – Ken Olsen, president of Digital Equipment Corporation (1977)

"640 K [of computer memory] ought be enough for anybody."
    – Bill Gates (1981)

  • 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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