Microsoft decided to open up its Virtual Hard Disk specification for free.
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.