I've been told it has to exist but where? operating system windows 7 pro. my dvd is drive D:, documents on drive C: gw basic is there. I get only one return from dosbox that drive doesn't exist.

loaded dosbox. trying to mount a drive (mount d d:\-t cdrom) comes back with d doesn't exists. no matter what drive I enter same result. tried (mount c c:\documents\gwbasic) same thing c doesn't exists. what am I doing wrong