VHD (Virtual Hard Disk) is a file format which represents a virtual hard disk drive (HDD). It may contain what is found on a physical HDD, such as disk partitions and a file system, which in turn can contain files and folders. It is typically used as the hard disk of a virtual machine.
VHDX is a Hyper-V virtual hard disk file format. VHDX has a much larger 64 TB storage capacity than the older VHD format 2TB limit. It also provides data corruption protection during power failures and optimizes structural alignments of dynamic and differencing disks to prevent performance degradation on new, large-sector physical disks.
When you mount a .vhd or .vhdx file, it will be added as a drive in This PC to open it from.
This tutorial will show you how to create an elevated task to auto-mount a VHD or VHDX file at startup for all users in Windows 8.1 and Windows 10.