Floppy Disk Drives / Mitsubishi M4855-112U / Modification

Homepage

Technical specifications (original)

Formfactor 5.25"
Capacity (DOS) 1.2 MByte (2 x 80 x 15 x 512 = 1.228.800 Byte)
Sides (Heads) 2
Tracks/Side 80
Sectors/Track 15
Byte/Sector 512
RPM / DataRate 360 / 500 KByte/s

Technical specifications (modification)

Formfactor 5.25"
Capacity (DOS) 720 KByte (2 x 80 x 9 x 512 = 737.280 Byte)
Sides (Heads) 2
Tracks/Side 80
Sectors/Track 9
Byte/Sector 512
RPM / DataRate 300 / 250 KByte/s

The overlooked modifications

Actually I wanted to buy a 5.25 inch 1.2 MB drive, but I got one with 720 KB. But a M4855 with 720 KB was never produced. Unfortunately I had overlooked the following modification.

This modification sets the rotational speed amongst others permanently to 300 RPM. It therefore makes no sense to work with a data rate other than 250 KByte/s.

Basically, the drive can still write at 500 KByte/s, but this data rate is intended for 360 RPM, not for 300.

Mitsubishi M4855-342 with modification
M4855-342 with modification

Now the M4855 is comparable to the Mitsubishi M4853 or TEAC FD-55F, both: DS, QD, 300 RPM, 250 KB/s, 96 tpi, 720 KByte.

mini-floppy drives
Mini floppy drives [mt88, p.146]

The M4855 is the successor of the M4854 (both HD), which is a pure 1.2 MB drive with 77 tracks. The M4855 has 80 tracks. The M4854 can be used instead of an 8 inch drive because it has the same parameters.

My modified M4855 is now only usable for CP/M computers. Here the 720 KB format with 5.25" is often used.