VMware is restricting the role that Microsoft can play at its virtualization user conference because Microsoft, like Citrix, is a VMware rival, Microsoft said.

Based on the agreement Microsoft signed in order to exhibit at the show, "we don't believe we have the right to demo our products in the booth. This decision runs counter to Microsoft's geek culture, as you can imagine, but we've also become more pragmatic over the years," said Patrick O'Rourke, Microsoft group product manager for Windows infrastructure, in a blog post.

According to O'Rourke, the agreement read in part:

Sponsors and exhibitors must market or demonstrate products on the exhibition floor and in the sessions which are complementary to VMware products and technologies. Complementary products and services are defined as products/services that do not overlap/substitute with VMware's products/capabilities, and help expand the reach and solution scope of VMware's capabilities solely as deemed by VMware.

That's a big contrast to last year, when Microsoft used the show to hype its own hypervisor.