A server farm (or server cluster, also called a data center) is a collection of computer servers usually maintained by an enterprise to accomplish server needs far beyond the capability of one machine. Server farms often have backup servers, which can take over the function of primary servers in the event of a primary server failure.
Server farms are typically co-located with the network switches and/or routers which enable communication between the different parts of the cluster and the users of the cluster.
The computers, routers, power supplies, and related electronics are typically mounted on 19-inch racks in a server room or data center.