【Mitsubishi Electric】 M2850 Disk Pack Unit

This was a medium-capacity removable magnetic disk unit announced in 1975 by Mitsubishi Electric. It achieved outstanding cost performance while using the same high-density recording/playback technology as high-capacity removable magnetic disk units such as the M836 and M2837. It was used for data files of mid/low-end machines of the COSMO Series, and for office computers and minicomputers.

This unit had the following features:

  • There were 5 disks in the disk pack, and the entire unit was a lightweight 5kg, including the top and bottom cover. It was designed to be easy to handle and inexpensive.
  • The positioning system was a closed-loop track-following servo system using a voice-coil-type DC linear motor. It achieved high-precision and high-speed positioning, and realized 50MB capacity while retaining compactness.
  • The unit had a rational dust-prevention and cooling system which cooled the disk pack with air from which 99.9985% of dust particles larger than 0.3μm had been removed. This air was also used to prevent dust in the carriage way and to perform cooling of the linear motor.
  • Each function was modularized, and this enabled access from the top, bottom, left and right during maintenance. The unit also had self-diagnostic functions.
  • It used the same controller as 100MB and 200MB high-capacity magnetic disk units.
  • The system was designed with interlock actuation to prevent danger and data destruction while the disk pack was rotating, and to prevent infiltration of dust when the power was OFF.
  • Expansion and maintenance were easy due to the 1 spindle/1 box structure.
Main Specifications of M2850 Disk Pack Unit
Unit memory capacity 54.3MB
Positioning time Min. 10ms,Max. 55ms,Average 30ms
Rotation speed 3,600rpm
Recording system MFM
Bit density 4,040bit/inch
Track density 370track/inch
Data transfer speed 806Kbyte/s
External dimensions(Height×Width×Depth) 800mm×500mm×900mm
Weight 150kg

In 1978, Mitsubishi announced the M2851F, which achieved a memory capacity of 82.1MB by increasing bit density by 1.5 times to 6,060bit/inch.

M2850 Disk Pack UnitM2851F Disk Pack Unit