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.More info over here.
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.
Microsoft opens up Virtual Hard Disk
Posted on Friday, October 20 2006 @ 7:22 CEST by Thomas De Maesschalck