In computing, Xen (pronounced /ˈzɛn/) is a virtual-machine monitor for IA-32, x86-64, Itanium and ARM architectures. It allows several guest operating systems to execute on the same computer hardware concurrently. The University of Cambridge Computer Laboratory developed the first versions of Xen; as of 2010[update], the Xen community develops and maintains Xen as free software, licensed under the GNU General Public License (GPLv2).
Xen systems have a structure with the Xen hypervisor as the lowest and most privileged layer.[1] Above this layer come one or more guest operating systems, which the hypervisor schedules across the physical CPUs. The first guest operating system, called in Xen terminology "domain 0" (dom0), boots automatically when the hypervisor boots and receives special management privileges and direct access to all physical hardware by default. The system administrator can log into dom0 in order to manage any further guest operating systems, called "domain U" (domU) in Xen terminology.
Modified versions of Linux, NetBSD and Solaris can run as the dom0. Several modified Unix-like operating systems may function as guest operating systems (domU); on certain hardware, as of Xen version 3.0, unmodified versions of Microsoft Windows and other proprietary operating systems can also run as guests if the CPU supports x86 virtualization (such CPUs include Intel VT-x and AMD-V).[2]
