【Mitsubishi Electric】 M4875 Hard Disk Unit

This was an 8-inch hard disk unit commercialized by Mitsubishi Electric in 1985. It was equipped with a thin-film head, and thereby achieved high recording density and a high memory capacity of 408MB.

The features of this unit were as follows:

  • 14,100BPI was achieved by combining a thin-film head with a coated disk, and using a 2-7 RLLC (Run Length Limited Coding) modulation system.
  • An easy-to-use interface was provided by adding diagnostic functions to the mainstream SMD interface.
  • It enabled high-speed data transfer at 1.81Mbyte/s.
  • The units were compact, and two units could be mounted side-by-side in a 19-inch rack.
  • High-reliability design enabling maintenance-free and inspection-free operation for 5 years or 20,000 hours, whichever came sooner.
Main Specifications of M4875 Hard Disk Unit
Unit memory capacity 408.5MB
Side capacity 31.43MB
Track capacity 30,720byte
Number of disks 8
Number of memory capable sides 13
Number of cylinders 1,023 + 1CE
Recording system 2-7 RLLC
Bit density 14,100bit/inch
Track density 1,000track/inch
Data transfer speed 14.52Mbit/s(1.815Mbyte/s)
Positioning time Min. 4ms,Max. 37ms,Average 20ms
Rotational delay Average 8.47ms
Rotation speed 3,544rpm
External dimensions(Width x Height x Depth) 216mm×259mm×650mm
Weight 38kg

M4875 Hard Disk Unit