Warning, geek-central posting:

A year ago Microsoft moved the Virtual Hard Disk format under the Open Specification Promise. (Funny...another data format...hmmm...but I digress) The point of that announcement was to enable anyone interested in looking at how Microsoft stored images of virtual machines...they could do so. This was good for other vendors doing virtualization solutions as well as folks doing management software etc. etc.

Well, last week Microsoft announced that the hypercall API in Viridian (the Microsoft Windows Server virtualization technology) is moving under the OSP as well. Here is the Virualization Team Blog posting. Here is the Peter Galli story over at eWeek. Also, here is a link to the Windows Virtualization page, and the hardware virtualization page.  The point of this is to enable other software providers to build high-quality virtualization solutions that either use, or are highly interoperable with Windows virtualization technologies.

By using the OSP, it means that any developer, no matter what model they are using (Free Software, fully proprietary commercial, whatever), can work with this technology. The patents are useable for the specification in perpetuity with a promise never to sue for their use.

Once again, interop is not just about standards. This announcement highlights 3 of 4 integral parts of interop:

Products: what you build into your product (e.g. Microsoft building the Viridian technology into the next version of Windows Server) with APIs, etc. that support interop natively in the technology.

Community: who you work with on interop - MS has had work under way with Citrix, XenSource and Novell (for example) for a year or more, plus our broader community of ISV partners.

Access: to technologies - meaning using IP as a means for collaboration and allowing others to get to our stuff. The OSP accomplishes this - doing it for virtualization of the format and now the API will enable others to better interop with Microsoft stuff.

I thought one of the quotes included in this release process did a good job of pulling things together. This is from Simon Crosby, CTO of Citrix:

Citrix is committed to the delivery of value-added virtualization solutions for  the Windows platform, so interoperability with Microsoft's virtualization solutions is key to our success.  This is made possible by Microsoft's  open and progressive approach to licensing key technologies such as its VHD image format and the Windows Server Virtualization hypercall API...This will allow us to ensure that virtual machines created on XenServer will be compatible with Microsoft WSV when it is delivered as a component of Windows Server 2008.