VHD (file format)
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| Filename extension | .vhd |
|---|---|
| Developed by | Connectix / Microsoft |
| Type of format | Virtual machine disk image |
VHD (Virtual Hard Disk) is a file format which represents a virtual hard disk drive (HDD). It may contain what is found on a physical HDD, such as disk partitions and a file system, which in turn can contain files and folders. It is typically used as the hard disk of a virtual machine.
The format was created by Connectix for their Virtual PC product, known as Microsoft Virtual PC since Microsoft acquired Connectix in 2003.
Since June 2005, Microsoft has made the VHD Image Format Specification available to third parties under the Microsoft Open Specification Promise.
A Virtual Hard Disk allows multiple operating systems to reside on a single host machine. This method enables developers to test software on different operating systems without the cost or hassle of installing a second hard disk or partitioning a single hard disk into multiple volumes. The ability to directly modify a virtual machine's hard disk from a host server supports many applications, including:
VHDX was added in Hyper-V in Windows Server 2012 to add larger storage capacity, data corruption protection, and optimizations to prevent performance degradation on large-sector physical disks.
VHDs are implemented as files that reside on the native host file system. The following types of VHD formats are supported by Microsoft Virtual PC and Virtual Server:
Significant benefits result from the ability to boot a physical computer from a virtual hard drive:
Native VHD Boot refers to the ability of a physical computer to mount and boot from an operating system contained within a VHD. Windows 7 Enterprise and Ultimate editions support this ability, both with and without a host operating system present. Windows Server 2008 R2 is also compatible with this feature.
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