【Fujitsu】 FACOM 621 Magnetic Drum Unit

Completed in 1960, the FACOM 621 was a magnetic drum unit used as auxiliary memory for the FACOM 222 large computer from Fujitsu. A magnetic core and magnetic drum unit were used as the main memory unit for the FACOM222P prototype, but the FACOM 621 was newly developed as an auxiliary memory unit for the commercial FACOM 222A, based on the technology of the D101 magnetic drum unit. The distinguishing feature of this unit is that it was an external memory unit with the same function as an internal memory unit. There were two types of FACOM 621: a unit with one built-in magnetic drum, and a unit with two built-in magnetic drums.

The FACOM 622 magnetic drum unit was developed as an improvement of this unit, and was used as an auxiliary memory device for the FACOM 231 and FACOM 230 (230-30).

Specification of FACOM 621 and 622 Magnetic Drum Units
  FACOM 621 FACOM 622
Completion date 1960 Around 1964
Memory capacity One drum:650,000bits
(10,000 words)
Two drums:1.3 million bits
(20,000 words)
262,144 digits
(1 digit=6 bits. On the drum, a space comprised of one bit was inserted before and after each 6 bits.)
Access time 10.5 ms(50Hz) 10.3 ms
Rotation speed 2,950 rpm(50Hz) 3,000 rpm(50Hz,60Hz)
Data transfer speed 155Kdigit/s 50Kdigit/s(400kb/s)
External dimensions (mm) 1,440(W)×640(D)×1,760(H) 900(W)×690(D)×1,760(H)
Connected systems FACOM 222A FACOM 231, FACOM 230(230-30)

FACOM 621 Magnetic Drum Unit