VHDX (Hyper-V virtual hard disk)
VHDX is a Hyper-V virtual hard disk (VHD) format found in Windows Server 2012.
The main advantage of switching to VHDX is its increased storage capacity of 64 TB (terabytes), instead of VHD's standard storage limit of 2 TB. Other advantages of VHDX include file corruption protection and the ability to create differencing disks.
VHDX files are not compatible with previous versions of Windows Server. However, the conversion process from VHD to VHDX is simplified with Windows Server 2012.