A VHD file contains a virtual hard disk image used by Microsoft Windows Virtual PC, a Windows virtualization program. It stores the contents of a hard disk of a virtual machine (VM), which may include disk partitions, a file system, files, and folders. VHD files may be used to install multiple operating systems on a single computer, test software programs, or run older applications.
The VHD Image Format Specification has been available as a royalty-free license since June, 2005. The VHDX format was introduced in 2012 as an extension of the VHD format. Virtual hard disks saved in the VHDX format are stored in .VHDX files.
NOTE: You can examine the contents of a VHD file manually by using 7-Zip.