Virtualization software, the kind that lets you run multiple operating systems at the same time, is getting a big boost from Microsoft. The company is allowing developers to use its Virtual Hard Disk (VHD) specification for free and without any licenses. The terms are quite simple with Microsoft saying, "The specification(s) could be used for free, easily, now and forever."

VHD stores information from the virtual operating systems inside of a single file on the hard drive. Essentially the virtualization software tricks the virtual operating system into thinking that the file is an actual hard drive. Other virtualization programs like VMWare use similar types of files.

The opening of the specification would allow developers to make new applications to monitor and manage virtual operating systems. Microsoft's pledge to never sue or charge for the specification comes from its new Open Specification Promise (OSP) initiative launched last month. So far Microsoft has added 38 other specifications with similar free licensing terms.