Sun will begin supporting Xen virtualisation in OpenSolaris in the next four months, with support in Solaris 10 in the first half of next year, the company said this week.

Sun will release working Xen support code in July. This code will give OpenSolaris the ability to run on Xen as a "Domain 0" (Dom0), or host, system, with support for 32-bit and 64-bit guest (DomU) Solaris systems.

OpenSolaris will get full Xen support by October, which will be extended to Solaris 10 in the first half of 2007, Sun said.

Under Xen, a virtualised machine is called a "domain," and operating systems must be modified at the kernel level to be fully virtualised - an approach called paravirtualisation that is designed to allow for maximum performance. The Dom0 system is fully virtualised, but has direct access to hardware, unlike DomU systems.

So far, Linux operating systems such as SUSE Linux Professional 9.3, the upcoming Suse Linux Enterprise 10 and Red Hat's Fedora Core 3 and 4, have been modified for Xen support. Operating systems such as Windows can run as a host system without modifications using virtualisation technology found in newer Intel chips and upcoming AMD chips.

Virtualisation is expected to revolutionise the use of operating systems, applications and even malware once it goes mainstream. Xen, developed at the University of Cambridge, is an open-source competitor to virtualisation providers such as VMware. Sun also provides its own container technology, but said it plans to provide users with the ability to mix and match.

Sun initially got Solaris working with Xen in a rudimentary form in July 2005. In February 2006 Sun released the first, early OpenSolaris-on-Xen code.

"Running on Xen, OpenSolaris is reasonably stable, but it's still very much 'pre-alpha' compared with our usual finished code quality," wrote Sun engineer Tim Marsland in his blog at the time. "Installing and configuring a client is do-able, but not for the faint of heart."