Over two years ago, Microsoft and Novell signed an interoperability deal. Part of this agreement was a patent deal that suggested that Linux infringed on Microsoft's IP. Since then, Microsoft has signed a number more of these deals with various companies, but the Novell one is still the most famous. Now, Red Hat has entered in to an interoperability agreement with Microsoft, too, but this time they left out the patent deal part. Instead, this deal covers virtualization support.