1. A programmable machine that receives input, stores and manipulates data, and provides output in a useful format.
2. An apparatus that receives, processes, and presents information.

The two basic types of computers are analog and digital.

Although generally not regarded as such, the most prevalent computer is the simple mechanical analog computer, in which gears, levers, ratchets, and pawls perform mathematical operations; for example, the speedometer and the watt-hour meter (used to measure accumulated electrical usage).

The general public has become much more aware of the digital computer with the rapid proliferation of the hand-held calculator and a large variety of intelligent devices and especially with exposure to the Internet and the World Wide Web.