With Windows 8 and Windows Server 8 Microsoft released a new file format for Virtual Hard Disk called VHDX.
The VHD format, which was availible since 2005 (Microsoft Virtual PC) and is now used by Microsoft Hyper-V and other Hypervisor, had some limitations.
The latest version of the VHD format was limited to 2TB of size and a block file size of 512bytes.
Now with VHDX Microsoft kills this limitations and brings some other improvements:
- Supports up to 16TB size
- Supports larger block file size
- improved performance
- improved corruption resistance
At this time you can use the VHDX format only with Windows 8 and Windows Server 8. But you can convert VHDs the VHDX format and VHDX disks back to VHDs.