VHD files under win7 system and their different types

1. What is a VHD file? First, Microsoft's VHD file format is a virtual machine hard disk, which can be compressed into a single file and stored on the host machine. On the file system, it mainly includes the system files required for the virtual machine to boot.
About VHD application: Virtual PC is a kind of windows virtual machine, it can virtualize various versions of windows, one windows should be installed on a hard disk partition, and it is virtual windows, it is impossible to draw a hard disk separately. The partition is installed for it, so the system files needed to boot it are compressed into a VHD format file on the hard disk.
The VHD format will also be used for Microsoft Windows Server 2008 R2 and Microsoft Windows 7, including hypervisor-based virtualization technology - Hyper-V. Hyper-V can operate VHD &mdash offline; allowing administrators to securely access the system through a VHD file, and administrators can access and perform some offline management tasks on virtual files (VHDs).
The VHD format is also available in the Business, Enterprise and Ultimate editions of Windows Vista for full system backup.
Second, multiple types of VHD files
1, fixed VHD
Fixed VHD files are assigned virtual disk size is the virtual disk size specified when creating VHD. For example, if you create a virtual hard disk that is 2 GB in size, the system creates a file that is approximately 2 GB in size, some of which is used for the internal VHD structure. The size of a fixed VHD does not change as data is written to the virtual hard disk.
2. Scalable or Dynamic VHD
At any given time, the size of an extensible or dynamic VHD file is the same as the actual data size written to the file. As more data is written, the file is dynamically increased. For example, a file that supports a 2 GB virtual hard disk is initially about 2 MB in the host file system. As data is continuously written to this virtual hard disk, the file grows until it reaches the 2 GB capacity limit.
3. Difference VHD
Difference VHD is similar to a dynamic VHD, but only contains modified virtual disk blocks of the associated parent virtual disk. The differential VHD is linked to a specific parent VHD, called a child VHD. The parent VHD file is read-only; all modifications are made to the child VHD. The VHD file type of the parent VHD can be any of these three VHD types, including another differential VHD. Multiple sub-VHD files can form a differential chain.