A server is a computer program or a device that waits for requests from other devices or software (called "clients") and responds to them. A server typically processes data. The purpose of a server is to share data or resources among clients. The clients may run on the same computer or may connect to the server over a network. Typical computing servers are database servers, file servers, mail servers, print servers, web servers, game servers, and application servers. Designating a computer as "server-class hardware" implies that it is more powerful and reliable than standard personal computers or is specialized for performing the server's role. Servers may be composed of large clusters of relatively simple, replaceable machines.

History

The use of the word server in computing comes from queuing theory, where it dates to the mid 20th century, being notably used in Kendall (1953) (along with "service"), the paper that introduced Kendall's notation. In earlier papers, such as the Erlang (1909), more concrete terms such as "[telephone] operators" are used.