【Fujitsu】 M2235 Magnetic Disk Unit

The M2235 magnetic disk unit was a Fujitsu magnetic disk unit for OEM which employed a 5.25-inch disk. It was completed in October 1983.

At the time, sophisticated "intelligence" functions such as Chinese characters, diagrams, audio, and image processing had been added to computer systems in offices, and mini floppy disk units were inadequate in terms of capacity and speed. Thus, there was a strong need for compact, inexpensive, high-performance files. The 5.25-inch disk unit, which maintained compatibility with mini floppy disk units in terms of external dimensions, mounting dimensions and voltage conditions etc., was developed under these circumstances. Fujitsu had developed the M223x Series of magnetic disk units (called "micro disks" at the time) based on technology for 8-inch disks. These disk units came in 6 types: the M2231 (2 disks, 6.6MB) and M2232 (3 disks, 10MB) which used 2 or 3 disks and were completed in June 1982; and the M2230 (1 disk, 6.6MB), M2233 (2 disks, 13.3MB), M2234 (3 disks, 20MB) and M2235 (4 disks, 26.6MB) which doubled the number of cylinders. These units had the following features:

1) External dimensions and mounting dimensions were made compatible with mini floppy disk units.
Mechanisms were simplified and miniaturized by, for example, using a direct drive DC motor for spindle rotation and a stepping motor to drive the magnetic access head.
2) Two types of interfaces were provided.
The industry standard ST506 (Seagate) interface was used with the AS type, and the SA4000 interface employed with 8-inch disks was used with the B type. This enabled flexible configuration through easy replacement of 8-inch disks and mixed connection with 8-inch disks.
3) SCSI was provided using a newly developed M1052A micro disk controller (directly mountable to the M223x series).

Fujitsu's 5.25-inch disks were called the Humming Series, and the 6th generation Humming-6, which was completed in April 1990, achieved a memory capacity about 44 times that of the first generation Humming-1.

5.25-inch Disk Unit, Specifications of Main Models
Model name M2235
Completion date October 1983 May 1984 October 1985
Memory capacity/unit
26.6 86.4 171.7
Data transfer speed
0.625 1.25
Average positioning time 85ms 33ms 25ms
Disk rotation speed 3,600rpm
Average rotational delay 8.4ms
Number of disks 4 6
Connection interface ST506,SA4000 ESDI,SCSI
  • Fujitsu's first 5.25-inch disk
  • Used VCM

Model name M2249
Completion date October 1987 August 1988 April 1990
Memory capacity/unit
389 778 1,165
Data transfer speed
1.25 1.8 3
Average positioning time 18ms 16ms 14ms
Disk rotation speed 3,600rpm
Average rotational delay 8.4ms
Number of disks 8
Connection interface ESDI,SCSI
Notes - -
  • Used MIG
    (Metal In Gap) head

Appearance of M2235 Magnetic Disk UnitM2235 Magnetic Disk UnitHere you can see the printed circuit board of the control section.M2235 Magnetic Disk Unit Here you can see the disk and head.