【Fujitsu】 FACOM 628K, L and R Magnetic Drum Units

drum unit, newly developed for Fujitsu's FACOM 230-25 and FACOM 230-35 mid-size general-purpose computers. The file devices available at the time were magnetic disk pack units, magnetic tape units and magnetic card units, and these were used in combination to exploit their respective advantages. Among such devices, magnetic drum units were introduced for system files, such as auxiliary memory to main memory. Because the magnetic drum units had comparatively large memory capacity, short access time, and outstanding reliability due to their mechanical characteristic.

The FACOM 628 came in 3 types, with different capacities, and had the following features:

(1) Magnetic heads for two tracks were housed in a single module to stabilize the head floating performance and reduce attaching process labor.
(2) Bit density was increased by narrowing the interval between floating magnetic head surface and drum surface.
(3) ICs were used extensively for control circuits, to improve reliability and reduce the size of the unit.
(4) Performance was doubled compared to the previous magnetic drum unit, without changing external dimensions.
Specifications of FACOM 628K/L/R Magnetic Drum Units
Completion date 1969
Memory capacity 262,144byte 524,288byte 1,048,576byte
Average access time 10 ms(50Hz)/8.4 ms(60Hz)
Data transfer speed 225 KB/s(50Hz)/269 KB/s(60Hz)
Drum Number of tracks 64 128 256
Rotation speed 3,000 rpm(50Hz)/3,600 rpm(60Hz)
Rotor dimensions 250ø×220mm (Ni-Co plating on aluminum cylinder)
Track pitch 0.6mm
Connected systems FACOM 230-25,FACOM 230-35

FACOM 628K/L/R Magnetic Drum UnitAppearance of FACOM 628K/L/R drum mechanism