Xen supports paravirtualization, in which the guest operating systems must have kernel extensions placed into their code so that they can cooperate with the Xen hypervisor (the virtualization software). Many mainstream Linux distributions like Red Hat, SuSE and Debian (along with many others as well) have those kernel extensions available and can thereby serve as the base operating environment for Xen (referred to as the host OS) as well as operating as guest OS systems. Xen 3.0, when running on the latest generation of chips from Intel and AMD, both of which have hardware extensions that better support virtualization, can run unmodified operating systems. In particular, this means that Xen 3.0, operating on machines with these chips, can host Windows guest systems.
This was first published in May 2006