Parallels, Inc. is a privately-held virtualization technology company with offices in the USA, Germany, UK, France, Japan, China, Russia and Ukraine. Parallels' US offices are in Seattle, WA and Herndon, VA. The company has more than 900 employees as of 2008.
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In computing, Xen is a virtual-machine monitor for x86, x86-64, Itanium and PowerPC 970 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 2009 the Xen community develops and maintains Xen as free software, licensed under the GNU General Public License (GPL2).
Xen vs ESX, 
