Virtual Hard Disk Specification
Microsoft is offering the Virtual Hard Disk (VHD) Image Format Specification available to third parties under a royalty-free license. This specification describes the Microsoft VHD format, currently used by Microsoft Virtual PC 2007 and Microsoft Virtual Server 2005 R2 and Hyper-V. Microsoft will use this format in the future versions of Microsoft Windows Server with hypervisor-based virtualization technology.
Microsoft VHD file format specifies a virtual machine hard disk that can reside on a native host file system encapsulated within a single file. The document focuses on how to store and modify the data in files on the host file system. It also includes identification/modification of parent hard disk image. It does not explain how hard disks interface with a machine.
The VHD format is agnostic to virtualization technology, host operating system, or guest operating system with which it is use, so it finds wider applications. VHD format can be used to move files between a VHD and the host file system. It provides backup and recovery, antivirus and security, image management and patching, disk conversion, and life-cycle management and provisioning.
Microsoft is providing access to the VHD Image Format Specification Document as a part of the Open Specification Promise (OSP). With OSP, interested parties can benefit from the Microsoft patented technology necessary to implement a list of covered specifications. The specifications are available for free. Registration is optional.
