Quoting from official announcement:
The recent release of NetBSD 2.0 marked a milestone in the development of the world’s most portable operating system. Every new release of NetBSD brings support for even more hardware platforms than the release before. But the 2.0 release included support for a remarkable new platform: the Xen virtual machine monitor. The NetBSD Foundation is proud to announce the continued work and intensive improvement of its support for Xen.
Xen supports virtualization of x86 hardware for complete separation of virtual machine environments with only minimal decrease in performance. NetBSD/xen can run in both privileged and unprivileged virtual machines under Xen 1.2, and in unprivileged virtual machines under Xen 2.0.
Christian Limpach committed the initial port of NetBSD to Xen to the NetBSD source repository on March 11th, 2004. Since then, enormous progress has been made, allowing the NetBSD Project to show their commitment to their development efforts by deploying NetBSD/xen within the project.
“We use virtualization with Xen every day on the foundation’s own servers,” says Thor Lancelot Simon, a developer and system administrator with The NetBSD Foundation. “It allows us to maintain multiple, isolated environments on a single 1U server. We aren’t naive enough to think that any system has perfect security; but Xen helps us isolate critical systems from each other, and at the same time helps keep our systems physically compact and easy to manage. When you combine virtualization with Xen with NetBSD’s small size, code quality, permissive license, and comprehensive set of security features, it’s pretty clear you have a winning combination, which is why we run it on our own systems.”
NetBSD 2.0 was the tenth major release of the freely available NetBSD operating system and the first to include NetBSD/xen, a port of the NetBSD kernel that runs under the Xen version 1.2 monitor. Significant work to run Xen version 2.0 has recently been completed by Manuel Bouyer and the next release of NetBSD will in all likelihood include this code. The Xen project already supplies a version of NetBSD/xen that runs under later versions of the Xen monitor.
Using Xen, a single machine can seamlessly switch back and forth between NetBSD/i386 and NetBSD/xen kernels on the same physical hardware, allowing easy development and testing; NetBSD/i386 binaries, as well as binaries compatible with NetBSD’s many operating system emulations, such as those for Linux and System V, run under NetBSD/xen without modification. At the same time, a NetBSD/xen system can coexist with other operating systems running in other Xen virtual machines; so Xen users can allocate resources to NetBSD, Linux, and other images running under Xen according to demand.