Xserve was a line of rack unit computers designed by Apple Inc. for use as servers. When the Xserve was introduced in 2002, it was Apple's first designated server hardware design since the Apple Network Server in 1996. It initially featured one or two PowerPC G4 processors, but was later switched over to the then new PowerPC G5, and subsequently switched again to two quad-core Intel Nehalem microprocessors.
The Xserve can be used for a variety of applications, including file server, web server or even high-performance computing applications using clustering – a dedicated cluster Xserve, the Xserve Cluster Node, without a video card and optical drives was also available. On November 5, 2010, Apple announced that the Xserve line would be discontinued on January 31, 2011 and replaced with the Mac Pro Server and the Mac Mini Server.
Read more about Xserve: Xserve G4, Xserve G5, Intel Xserve