MDR (Floppy Disk)
MDR Floppy Disk Format
The MDR disk format is used to store musical registration and song settings used in the Yamaha Electone range of electronic Organs, including EL40,60,70,80 & 90.
The MDR disk format is very close to a standard MS-DOS format. Some OS or computers refuse to read these disks when they have been formatted on the MDR, because the format is not exactly one of the standard DOS formats. This is not a problem: format a floppy disk on your computer and then record it with your MDR. Such a floppy disk is readable on your computer. (from )