Microsoft and Novell will enable virtualization for each other's server operating systems as part of the companies' ongoing alliance to make Windows and Linux more interoperable.

Microsoft Virtual Server 2005 R2 Service Pack 1 will let users host Novell's Suse Linux Enterprise Server 10 as a virtualized guest, and the next version of Windows Server, code-named Longhorn, will have the ability to host Novell's Linux OS as an enlightened guest using built-in virtualization technology.

In turn, Suse Linux Enterprise Sever 10, using Xen virtualization technology that is embedded in the OS, will be able to host Longhorn as a paravirtualized guest.

Enlightenment and paravirtualization are different terms that describe similar, but not identical, techniques to improve performance. An enlightened guest OS is modified to make it aware it's running on Windows Server virtualization. A paravirtualized guest OS is modified to make it aware it's running on the Xen hypervisor.

A virtualized guest OS running on Virtual Server 2005 R2 does not require modifications to make it aware it's running in a virtual machine. Thus, it is not "enlightened" or "paravirtualized."

Longhorn, the long-awaited update to Windows Server, is due in the second half of 2007.

Virtualization is just one of four key areas on which the companies said Monday they will focus their collaborative efforts this year. The other areas are Web services-based network management, directory interoperability, and document format interoperability.

In the Web services-based management area, Microsoft and Novell said that they will both incorporate WS-Management (Web services for management) in their products to enable OS management through Web services. Novell ZENworks Orchestrator and Microsoft System Center Operations Manager 2007 will both support WS-Management this year.

WS-Management is a specification of a Web services-based protocol for the management of servers, devices, and applications. Microsoft, Intel, Dell, and other companies published the spec in March 2005, and it was ratified by the Distributed Management Task Force for adoption as a preliminary standard in August 2006.

Novell also is working to develop an open-source implementation of WS-Management, the company said.

Microsoft and Novell already have introduced technologies to make communication between the global standard file format for office documents, ODF (Open Document Format for XML), and the default file format in Microsoft Office 2007, Open XML, easier. On Feb. 2, Microsoft announced the availability of the Open XML/ODF Translator for Office 2007, Office 2003, and Office XP. Later this month, Novell will release an Open XML/ODF Translator for the Novell edition of the OpenOffice.org open-source productivity suites.

On the directory and identity-management fronts, both companies continue to work on technologies to make their offerings in these areas interoperate, but they have not announced specific progress yet. Microsoft and Novell said they will offer a more detailed roadmap for how their directory and identity management products will interoperate later this year.

As part of the deal struck in March, Novell and Microsoft agreed, among other things, to co-develop technologies that would help Novell's Suse Linux and Microsoft's Windows OSes interoperate more seamlessly. The alliance between the two -- particularly Novell's payment to Microsoft for patents -- has inspired much controversy. Novell especially seems to have lost some credibility within the open-source community for joining forces with the proprietary software giant.