【Mitsubishi Electric】 M836 Disk Pack Unit

This was a high-capacity removable magnetic disk unit announced by Mitsubishi Electric in 1973. It was a equivalent of the IBM3330 magnetic disk unit, and had a memory capacity of 100MB per spindle and a high-speed positioning mechanism which required 30ms on average. This unit was used for data files for mid-size to large computers such as the MELCOM 7000 Series and COSMO Series.

This unit had the following features:

  • It exploited high-density magnetic recording technology to achieve a track density of 192track/inch and a bit density of 4040bit/inch, and used the MFM (Modified Frequency Modulation) system to achieve the high capacity.
  • Positioning at higher speed and precision was enabled by using a track-servo system which employed a linear motor in place of the conventional hydraulic positioning system.
  • A rotational position detection mechanism and high-reliability automatic maintenance functions reduced the burden on the disk controller and improved availability. Diagnostic programs enabled self-diagnosis.
  • By using Mitsubishi's unique self-pressing magnetic head technology, the system simplified and lightened the head pressing/holding mechanism, and realized faster access times.
Main Specifications of M836 Disk Pack Unit
Unit memory capacity 100MB
Track capacity 13,440byte
Positioning time Average 30ms
Rotation speed 3,600rpm
Bit density 4,040bit/inch(159bit/mm)
Track density 192track/inch(7.5Track/mm)
Data transfer speed 806Kbyte/s
Recording system MFM
Memory media IBM3336 or the equivalent
Disk diameter : 14inch(356mm)
Number of disks : 10 + 2(protected)
Data recording sides : 19
servo sides: 1
Number of cylinders : 404 + 7(spare)
Weight : 9kg
External dimensions(Width x Height x Depth) 640mm×1,100mm×950mm
Weight 250kg

The M2837, its enhanced model, was announced in 1975. It achieved a memory capacity of 200MB by doubling the track density to 370track/inch, and setting the number of cylinders to 808 + 7 (spare).
The M2838F, further enhanced model, was announced in 1979. It achieved a memory capacity of 300MB by increasing the bit density 1.5 times to 6,060bit/inch, and adopting a track capacity of 20,160 bytes.

M836 Disk Unit