https://technet.microsoft.com/en-us/sysinternals/ee656415.aspx
Important restrictions
Note: Virtual PC supports a maximum virtual disk size of 127GB. If
you create a VHD from a larger disk, even if you only include data from a
smaller volume, it will not be accessible from a Virtual PC VM.
In addition
Virtual PC doesn't support the Multiprocessor Specification, which means that it
won't be able to boot VHD's from multiprocessor Windows XP and Windows Server
2003 systems.
If you create a VHD from Windows XP or Windows Server 2003
and plan on booting the VHD within Virtual PC, select the "Prepare VHD for use
in Virtual PC" option, which ensures that the HAL (Windows Hardware Abstraction
Layer) installed in the VHD is compatible with Virtual PC.
Check this post out for a VHD vs VHDX comparison
https://www.netwatch.me/2015/03/19/vhd-vs-vhdx-hmm-whats-the-difference/
Check this post out for a VHD vs VHDX comparison
https://www.netwatch.me/2015/03/19/vhd-vs-vhdx-hmm-whats-the-difference/
