【Mitsubishi Electric】 M-811 Magnetic Disk Unit

Announced in 1968, this was Mitsubishi Electric's first fixed head magnetic disk unit. The unit achieved high-reliability at an extremely low price by adopting a floating head and simplifying the mechanism. It was used with office computers, minicomputers and other small computers, as well as with automatic testers.

This unit had the following features:

  • The floating head followed the disk well, and temperature control to maintain a constant gap between head and disk was unnecessary.
  • A head was provided for each track, so access time was short.
  • Although the unit was compact and lightweight, it could store 270,000 bits or 540,000 bits, and bit cost was low.
  • The system could withstand long-term use due to a hard protective coating of the disk and head, a sealed structure to prevent dust, and anti-corrosion treatment of all parts.
Main Specifications of M-811 Magnetic Disk Unit
  M-811-1 M-811-2
Memory capacity 266,240bit 532,480bit
Track capacity 8,320bit 8,320bit
Recording system NRZ system or PM system
Number of data tracks 32 64
Number of timing tracks 4 4
Magnetic disks 8-inch 1side 8-inch 2 sides
Disk rotation speed 3,000/3,600rpm
Rotational delay Average 10/8.3ms
Data transfer speed 416/499Kbit/s
External dimensions(Diameter×Hight) 256mm×250mm
Weight 15kg

In 1972, Mitsubishi Electric announced further members of this Series: the M-810 with a memory capacity of 100,000 bits, the M-814 with a memory capacity of 1 million bits, and the M-824 with a memory capacity of 2 million bits. The M-810 used a 6-inch magnetic disk and was smaller, with a diameter of 200mm, and the M-814 used an 8-inch magnetic disk and had an increased track capacity of 16,650 bits. The M-824 used a 12-inch magnetic disk, and had an increased track capacity of 33,250 bits.

M-811 Magnetic Disk UnitM-814 Magnetic Disk Unit