Xen-enabled Linux relies on Xen, an open-source virtual machine monitor that uses paravirtualization to achieve what XenSource claims is a tenfold performance increase over alternative virtualization implementations. The drawback is that "guest" operating systems need to be ported to work with Xen, but Linux distributions like Novell's SuSE and the RedHat-sponsored Fedora have implemented Xen support. The advent of hardware virtualization via Intel's VT-x and AMD's Pacifica has allowed unmodified guest operating systems to run on Xen, but host OS compatibility is still restricted and currently excludes Windows. Microsoft's partnership with XenSource will remedy this situation.
Going by Microsoft's press release, a beta version of Windows Server virtualization will come out by the end of this year. The final version will follow within six months of the release of Windows Server "Longhorn," which is due out in late 2007.