A computer connected to a network that other computers may or may not access. Unlike other computers on a network, a server is a dedicated computer set up for one or more purposes. For example, a user may setup a server to authenticate and allow or prohibit users from accessing a network, send/receive e-mail, manage print jobs, or host a website. For example, the Computer Hope web page is hosted on a server. In the picture, is an example of cluster of rack mountable computers at the NCSA/University of Illinois.
Because servers commonly serve a need that's required 24/7 they're often never turned off and when fail cause the network users or company a great deal of problems. Some server failures can cause a company and its employees to come to a complete halt in their work until they return. Because of this, servers are commonly high-end computers and are setup to be fault tolerant.