【Fujitsu】 FACOM 493 Magnetic Disk Unit

The FACOM 493 was a magnetic disk unit from Fujitsu which employed a non-portable disk module. It was completed in October 1978.

In order to increase the memory capacity of a magnetic disk, it is crucial to improve recording density on the media. However, with disk packs employing the portable media system, density increases are limited due to the need to secure a margin for reading data written with other equipment, and the need to ensure airtightness against dust.

Therefore, Fujitsu developed the FACOM 493 magnetic disk unit, which fastened the media and the disk head to the unit of disk. This change from a portable disk to non-portable disk system was acceptable because the memory capacity of magnetic disk units had been dramatically improved, and there was less of a need to frequently change disk packs during operation.

Use of the non-portable disk system (the disk head and the media was packed) with this model was the starting point for developing the high-capacity, high-performance technology of subsequent magnetic disk units. The FACOM 493 came in an A2 and C2 model equipped with an adapter for connection with a controller, and a B2 model with no adapter. All models were equipped with two units of disk, and had a memory capacity of 635Mbyte for the unit overall. In April 1980, Fujitsu completed the FACOM 496 which had logical compatibility with the FACOM 493, while having two times the memory capacity of the FACOM 493.

For mid-size and small computers, on the other hand, there was high demand for portability due to cost issues, and Fujitsu developed the FACOM 467 disk pack unit (Winchester disk type) which integrated the disk media and the disk head, and this integrated unit was adopted for a replaceable structure. This made it possible to suppress variation due to individual differences in media and heads, and although this approach increased capacity, products of this type did not last long.

Specifications of FACOM 493 and 496 Magnetic Disk Units
  FACOM 493A2/B2/C2 FACOM 496 (Reference) FACOM 467
Completion date October 1978 April 1980 March 1977
Disk Memory capacity 317.5Mbyte 635Mbyte 70Mbyte
Disk type Fixed disk Winchester
(Replaceable data module)
Disk diameter 14inch
Positioning time 20ms 20ms
Rotation speed 3,600rpm 2,970rpm
Average rotational delay 8.4ms 10.1ms
Data transfer speed 1.198Mbyte/s 885Kbyte/s
Memory capacity/unit 635Mbyte 1.27Kbyte 140Mbyte
Main connected systems Large FACOM M-100 Series FACOM M-130F/140F/150F

FACOM 493 Magnetic Disk UnitFACOM 467A2 Disk Pack Unit