super mrc os was designed to work with the mc - 500 mk2. i don't recomend useing it with the mc - 300. actually im might not work at all ! take a look at my review of the mc - 500 at
http://www.harmony-central.com/Synth/Data/Roland/MC-500-01.html

i explane the problems there, basicly it causes the mc to use the floppy for virtual memmory causeing the disk drive to run every time you change modes. thats a fast way to burnout your floppy drive