The surprise announcement yesterday from Red Hat and Microsoft appears straightforward. In basic terms, they promise to help companies run Red Hat Enterprise Linux and Windows Server on the same computer servers, using virtualization technology. What's remarkable is what's missing. The companies say there's no patent agreement as part of the deal.

"The agreements contain no patent or open source license components," writes Red Hat's Scott Crenshaw. "There are no financial clauses beyond simple certification testing fees. These are straightforward certification and validation agreements."

That's a departure from Microsoft's deal with Novell, the Red Hat rival. The Novell agreement includes a provision in which the companies agreed not to sue each other's customers for patent violations. Many people in the open-source community see that as Novell implicitly endorsing Microsoft's contention that Linux and other open-source programs violate the Redmond company's patents. Novell disputes that viewpoint, but the deal is generally unpopular in the open-source world nonetheless.

In contrast, Red Hat's announcement with Microsoft is winning praise.

"Congratulations to Red Hat for refusing to buckle on this vital matter, and to Red Hat Legal for working out the details, and a tip of the hat to Microsoft, for facing reality and doing the right thing," writes the popular Groklaw blog.

Why did Microsoft do this now? Time will tell if there's more to the story, but here's the explanation from Microsoft's Mike Neil.

Let me say that I’m sure everyone reading this can appreciate the distance between Microsoft and Red Hat is measured in more than just the 2,900 miles between Redmond, WA and Raleigh, NC. Microsoft and Red Hat have competed for customers and partners for some time now and as platform vendors continue to compete in the marketplace. Yet, our customers have told us that technical support for server virtualization is an area we must work together. And that’s certainly understandable when you consider the fact that roughly 80% of the primary guest (in a VM) operating systems on x86 servers today come from Microsoft or Red Hat. Indeed, customer demand is the main driver behind these agreements with our competitor.

Also see posts by Matt Asay and Mary Jo Foley, and a Red Hat FAQ.