Xen Virtualization: Hypervisor (aka VMM aka Microkernel)
Xen is a virtual machine monitor for x86 that supports execution of
multiple guest operating systems with unprecedented levels of
performance and resource isolation.
This package contains the Xen Hypervisor. (tm)
Modern computers are sufficiently powerful to use virtualization to
present the illusion of many smaller virtual machines (VMs), each
running a separate operating system instance. Successful partitioning
of a machine to support the concurrent execution of multiple operating
systems poses several challenges. Firstly, virtual machines must be
isolated from one another: It is not acceptable for the execution of
one to adversely affect the performance of another. This is
particularly true when virtual machines are owned by mutually
untrusting users. Secondly, it is necessary to support a variety of
different operating systems to accommodate the heterogeneity of popular
applications. Thirdly, the performance overhead introduced by
virtualization should be small.
Xen uses a technique called paravirtualization: The guest OS is
modified, mainly to enhance performance.
The Xen hypervisor (microkernel) does not provide device drivers for
your hardware (except for CPU and memory). This job is left to the
kernel that's running in domain 0. Thus the domain 0 kernel is
privileged; it has full hardware access. It's started immediately after
Xen starts up. Other domains have no access to the hardware; instead
they use virtual interfaces that are provided by Xen (with the help of
the domain 0 kernel).
Xen does support booting other Operating Systems; ports of NetBSD
(Christian Limpach), FreeBSD (Kip Macy), and Plan 9 (Ron Minnich)
exist. A port of Windows XP was developed for an earlier version of
Xen, but is not available for release due to license restrictions.
In addition to this package you need to install the kernel-xen and
xen-tools to use Xen. Xen 3 also supports running unmodified guests
using full virtualization, if appropriate hardware is present. Install
xen-tools-ioemu if you want to use this.
[Hypervisor is a trademark of IBM]