What Does Hyper-V Virtual Hard Disk Mean?
A Hyper V virtual hard disk (VHDX) is a disk image file format used to create a virtual hard disk (VHD) within Windows Server 2012-based virtualization environments.
VHDX enables creating and provisioning virtual/logical disk storage space to virtual machines. It is an enhancement to the previously used VHD file format in Windows Server 2008.
Techopedia Explains Hyper-V Virtual Hard Disk
VHDX works as a typical virtual hard disk, but in reality it’s a file format. It can store data up to 64 TB, it enables creating differencing disks and has superior protection against disk corruption. It is created and managed using native Windows Server 2012 tools such as DiskPart, Hyper V Manager and Disk Manager.
The size/capacity of the VHDX for each virtual machine can be fixed or is dynamically adjusted based on requirements/usage. Although VHDX is not backward compatible, all previous VHD file formats can be converted to VHDX within the Windows Server 2012 OS environment.