VHD (file format)

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The Virtual Hard Disk Format ( VHD format, from the English Virtual Hard Disk virtual hard disk ) is a container file format and usually has the file extension ". Vhd ". It was originally developed by Connectix for Virtual PC and Virtual Server, evolved since its acquisition by Microsoft and supported on Windows 7 directly in the operating system.

Technical details

Virtual disks in VHD format can be created with either a fixed or a dynamically expanding size from Windows 7 via the included therein Disk Management and with the command line tool diskpart. The maximum size for dynamic and differential VHDs is 2 Tebibyte that is not limited to a maximum of size VHDs fixed length, however, limited in practice by the maximum file size of 16 Tebibyte per file (for NTFS). In the dynamic size when generating only the maximum size is set, which must not exceed the container file. In the fixed size, the file is given exactly as big as when creating - and it does not matter whether it is actually filled with data or not.

With the development of Windows 8 's file format has been extended and this extension (English enhancement ) as " VHDX " named. That should then be possible to create disk images with a maximum size of up to 16 Tebibyte. Moreover, it was extended with Windows 8 Explorer accordingly, thus to be accessed directly on such dumps.

The biggest drawback is that the dynamically growing or differential hard drive afterwards ( with Windows tool ) can not be extended or reduced. Only the hard disk of fixed size can be expanded later. However, there are external tools (such as the VHD Resizer ) is available. In addition, the data can also be manually copied into larger or smaller (virtual) hard drives and so quasi whose size can be changed, but this can be very time consuming.

Support

The file format is not only virtual machines like Virtual PC and Virtual Server or operating systems like Windows 7 and Windows Server 2008 and the Windows Automated Installation Kit, as well as many others ( partly free ) programs, such as VirtualBox or 7 -Zip, support.

In addition to the VHD format as the default file format - generally for memory dumps, and especially about for backups - are taken up and used in the virtualization of Microsoft 's portfolio.

The program Disk2vhd, Windows Sysinternals, the data of physical disks can be copied to virtual disks ( images ) in order to integrate them, for example in VirtualBox and then migrate all the computers can.