You can't select the drive letter anywhere, it is somethin along the lines of, a cable actualy selecting the letter. If you have a floppy cable that can hook up multiple drives the "master" at the end would be drive A:, and the "slave" in the middle would be B:, there is and was no way to switch them around, the wire missing between A: and B: is what decided there letters. So it IS a physical limitation.