A computer is a programmable machine. The two principal characteristics of a computer are: it responds to a specific set of instructions in a well-defined manner and it can execute a prerecorded list of instructions (a program). 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.
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