Xen is an open-source paravirtualization technology that provides a platform for running multiple operating systems in parallel on one physical hardware resource, while providing close to native performance. Xen supports several operating systems—Linux, FreeBSD and NetBSD. The current version of Xen also supports the new generation of AMD Pacifica and Intel VT-x chipsets and can run an OS on these chips without any modifications by using a version of the hypervisor called the Hardware Virtual Machine (HVM). HVM mediates between the guest operating system and the hardware and passes on the calls made by the guest to the physical hardware. So you can run Microsoft Windows on these chips using Xen!
Xen was originally developed in 2003 at the University of Cambridge Computer Laboratory (http://www.cl.cam.ac.uk/research/srg/netos/xen/). There are both commercial and free versions of Xen. The commercial versions are built on top of the open-source version with additional enterprise...