Xen is a free software virtual machine monitor for IA-32, x86-64, IA-64 and PowerPC 970 architectures. It allows several guest operating systems to be executed on the same computer hardware at the sam... More

Xen is a free software virtual machine monitor for IA-32, x86-64, IA-64 and PowerPC 970 architectures. It allows several guest operating systems to be executed on the same computer hardware at the same time.A Xen system is structured with the Xen hypervisor as the lowest and most privileged layer . Above this layer are 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), is booted automatically when the hypervisor boots and given special management privileges and direct access to the physical hardware. The system administrator logs into dom0 in order to start any further guest operating systems, called domain U (domU) in Xen terminology. Modified versions of Linux, NetBSD and Solaris can be used as the dom0. Several modified Unix-like operating systems may be employed 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 be used as guests if the CPU supports VT technology. Xen originated as a research project at the University of Cambridge, led by Ian Pratt, senior lecturer at Cambridge and founder of XenSource, Inc. This company now supports the development of the open source project and also sells enterprise versions of the software. The first public release of Xen was made available in 2003. XenSource, Inc was acquired by Citrix Systems in October 2007. XenSource's products have subsequently been renamed under the Citrix brand: XenExpress was renamed XenServer Express Edition and XenServer OEM Edition (embedded hypervisor); XenServer was renamed XenServer Standard Edition; XenEnterprise was renamed XenServer Enterprise Edition.On 2007-10-22, Citrix Systems completed its acquisition of XenSource, and the Xen project moved to http://www.xen.org. This move had been under way for some time, and afforded the project an opportunity to make public the existence of the Xen Project Advisory Board (Xen AB), which currently has members from Citrix, IBM, Intel, Hewlett-Packard, Novell, Red Hat and Sun Microsystems. The Xen AB is chartered with oversight of the project's code management procedures, and with development of a new trademark policy for the Xen mark, which Citrix intends to freely license to all vendors and projects that implement the Xen hypervisor; the requirements for licensing will be solely the responsibility of the Xen AB.  [edit]  Less