It is a tool that allows you to resize a VHD (Virtual Hard Disk). VHD is Microsoft’s format for virtual disks, and is used by Virtual PC, Virtual Server, and Hyper-V. VHD Resizer can be used to enlarge or shrink virtual disks of all three virtualization solutions. Windows Vista and Windows 7’s system backup tools also use this format. However, it doesn’t make much sense to enlarge a backup image. There are also third party virtualization tools, such as VirtualBox, that support the VHD format.
VHD Resizer changes the size of the VHD, but not the size of the NTFS partition. Thus, if you access the VHD through a virtual machine, you just see a larger disk with additional unpartioned space. You have to use a partition management tool, like diskpart, to extend the partition. Only then can you make use of the full capacity of the virtual disk. Diskpart is a Windows command line tool.
Extending a partition with diskpart is very simple:
Launch diskpart on a command prompt.
Type “list volume.” This gives you the number of the volume that you want to extend.
Type “select volume volume-number.“
Download VHD Resizer from here