If you connect your drive to the computer you get the drive letter of the first free letter. that can differ between the systems you use. Some people want/need a fixed drive letter for their portable drive. So the idea of some people was simple: Mount the portable drive to a virtual drive. Windows itself got all tools (normally) onboard. It is done by subst.exe.
Since version 2.0 its possible to configure a drive letter. There is a INI file named VirtualDriveSet.ini, which is located in the application main folder. Modify the variable Driveletter to your choice.
add lable for virtual drive
add paf like ini handling
add configuration on first run
IF YOU USE A PAM MOD WITH EJECT FUNCTION, THE EJECT FUNCTION STOP WORKING AFTER STARTING VIRTUALDRIVESET!!!
cu & hf
ps: thx @ porwerjuice