For people who cwant to use old computers: the DREM (DRive EMulator) is a commercial FDD & MFM/RLL HDD emulator or MFM SSD.
DREM can either emulate floppy drives or hard drives. It uses SDcard for storage. It can emulate up to four (4) floppy drives. It can emulate one ST-506 / ST-412 hard drive, with an optional header, you can emulate up to two hard drives.