Xen FAQ General

What is Xen?

Xen is a virtual machine monitor (VMM) for x86-compatible computers. Xen can securely execute multiple virtual machines, each running its own OS, on a single physical system with close-to-native performance. You can find an overview of Xen at Xen_Overview.

I'd like to read some kind of overview about Xen

See the XenOverview wiki page and Category:Overview. Also check the following PDF documents (which are somewhat out-of-date):

• http://www.xen.org/files/Marketing/WhatisXen.pdf
• http://www.xen.org/files/Marketing/WhyXen.pdf
• http://www.xen.org/files/Marketing/NewtoXenGuide.pdf
• http://www.xen.org/files/Marketing/HowDoesXenWork.pdf

How is Xen licensed?

Xen is Open Source, and is released under terms of the GNU General Public License v2. Some Xen projects may contain licensing exceptions or a small number of files which are licensed under a GPL compatible license. If so, the source repository contains a COPYING file providing more information (see here for the COPYING file for the hypervisor).

Xen projects do not come with an End User License as the GPL suffices. There is however a trademark policy that restricts the use of the Xen brand to ensure that all Xen branded hypervisors are compatible and will run the same guest VMs. You can find the [http:/www.xen.org/files/XenTMPolicy2008June.pdf trademark policy here].

Operating systems or other applications written to use Xen's hypercall interface are not derived works of Xen, hence may be licensed differently.

Which OSes run on Xen?

To achieve such high performance, Xen requires that OSes are ported to run on it.

See Xen Dom 0 Kernels and Xen Dom U support

Does Xen support Microsoft Windows?

The paravirtualized approach we use to get such high performance has not been usable directly for Windows to date. However Xen 3.0 added Intel VT-x support to enable the running of unmodified guest operating systems, including Windows XP & 2003 Server, using hardware virtualization technology. Xen 3.0.2 and later support AMD Pacifica technology as well. Check to see if your CPU is among the list of HVM Compatible Processors, and if your motherboard is among the list of HVM Compatible Motherboards.

(Note: This does not necessarily mean, that just about _any_ OS runs in HVM Mode! Reports vary about getting *BSD to work in HVM mode, on the Mailing List there's only 1 success for OpenBSD (http://www.openbsd-france.org/ml/archives/msg02494.html), no success message for the others, but some problem reports)

Does Xen run on laptops?

Xen will typically run on laptops.

Which architectures does Xen support?

Xen currently runs on the x86, x86_64, IA64 (Itanium) and ARM architectures. On x86 Xen requires a "P6" or newer processor (that's any Intel or AMD x86 CPU purchased in the last seven years). Multiprocessor and multicore machines are supported, including support for Hyper-Threading (SMT). Support for x86/64 is available since Xen 3.0. We hope to add other architectures such as PPC.

32bit and 64bit

The 32bit and 64bit questions are many and more complex than you might think. Things can be 32bit, 32bit PAE or 64bit. There is the hardware, the xen hypervisor, the dom0 kernel and userland and the domU kernel and userland.

	32bit PAE Hypervisor
32bit PAE PV DomU	Yes
64bit PV DomU	No
32bit HVM DomU	Yes
64bit HVM DomU	No