Servers these days are physically similar to most other general-purpose computers, although their hardware configurations may be mainly optimized to fit their server roles, if they are dedicated to that role. Many use hardware identical or almost identical to that found in standard desktop PCs. However, servers run software that is often very different from that used on desktop PCs and workstations.

Servers should not be puzzled with mainframes, which are very large computers that centralize certain information-processing actions in large organizations and may or may not act as servers in addition to their other activities. A lot of large organizations have both mainframes and servers, although servers usually are smaller and much more frequent and decentralized than mainframes.