The arrangement marks a new level of cooperation between Windows and Linux-based systems.

The pact will enable Microsoft Windows Servers 2008 and 2003 to run as a supported, guest virtualized operating system on Red Hat Enterprise Linux 5. On the other side Red Hat Enterprise Linux 5 will now be a supported guest virtualized operating system on Windows Server 2008.

The interoperability deal between Red Hat and Microsoft comes as the nascent market for virtualization continues to grow and as customers increasingly ask for certified and supported solutions among vendors. The new deal will provide a competitive offering to Novell, VMware and Citrix’s XenSource, which all offer a varying degree of supported interoperability between Windows and Linux servers running as virtualized guests.

Mike Evans, a vice president of corporate development at Red Hat, told reporters on Monday that the lack of a fully certified and supported virtualized guest support between Microsoft and Red Hat has inhibited customers from broad adoption of virtualization technology.

“We’ve signed agreements for testing, validation and co-operative support for server virtualization,” Evans said during a conference call. “They are straight-forward agreements and there are no patent or licensing rights provided by these agreements. There are no financial clauses other than the certification and validation testing clauses.”

Evans stressed that the key to the deal was to enable customers to run Windows on Red Hat and vice versa in a supported manner.

The arrangement between Red Hat and Microsoft on virtualization is different than the a joint-interoperability pact Microsoft and Novell struck in 2006.

That deal covered joint efforts to further Windows and Linux interoperability and included patent provisions. As of late 2008, Novell claimed that the Microsoft interoperability deal was worth over $340 million. Microsoft’s deal with Red Hat is much more narrow.

“You can think of the Red Hat agreement as more of a one dimensional agreement,” said Mike Neil, general manager of virtualization strategy at Microsoft. “With Novell it was more of a multi-dimensional agreement, where we have technical collaboration, patent co-operation and business collaboration. The Red Hat agreement is focused primarily on validation and support within the virtualized space.”

Microsoft has alleged that Linux and open source technologies infringes on over 200 Microsoft patents. The Novell deal has a patent covenant that protects Novell’s SUSE Linux users from any potential litigation. Red Hat has steadfastly refused over the years to enter into a similar patent deal with Microsoft, even though Microsoft CEO Steve Ballmer has claimed that Red Hat “owes” Microsoft.

In an interview with, Evans explained that the latest pact is designed for Red Hat Enterprise Linux systems running Microsoft’s Hyper-V virtualization technology. (This isn’t the first time that Red Hat has been enabled for virtualized Windows systems. VMware’s hypervisor currently supports Red Hat Enterprise Linux running on Windows.)

What the new deal does provide, according to Evans, is better testing and the ability to support both the Red Hat and Microsoft technology environments. Part of the deal is to provide support for customers whether running Windows on Red Hat Enterprise Linux or vice versa.

“You call the first company that you think you have the problem with, and if it can’t be solved, Microsoft or Red Hat will work with the other vendor to come to a resolution for the mutual customer,” Evans explained.

From a technical point of view Evans does not see any particular challenges in supporting Windows as a virtualized guest on Red Hat Enterprise Linux or vice versa.

“There are a number of customers running Windows on Red Hat Enterprise Linux today,” Evan said. “The primary advantage of the new agreements is that they allow us to formalize the testing support of these configurations.”