【Fujitsu】 FACOM 461B Disk Pack Unit

The FACOM 461B was a disk pack unit from Fujitsu which used a disk pack comprised of six 14-inch disks (same as IBM1316 or the equivalent), and was completed in 1964 for use with the FACOM 230-20 system.

The disk pack was made of magnetic recording disks with a removable structure, and disk pack units using this media combined the features of magnetic tape and magnetic drums, as indicated below.

1) Media was replaceable, so the unit had infinite memory capacity.

2) Data could be written and read in a random access fashion.

The FACOM 461B was equipped with an access arm comprised of 5 arms in a single unit. Each arm had two read/write heads. The arms were driven simultaneously by a hydraulic motor to enable access to 10 disk surfaces. (Both surfaces of disks were used, except the two outer side surfaces). One head was used for each disk. Each disk side was comprised of 203 tracks (of which 3 were spares), and each track was divided into 10 sectors (record length: 256 bytes).

Later, Fujitsu developed the redesigned FACOM 462K and FACOM 462K-1 which used the same disk pack, and reduced positioning time by employing an electric pulse motor in the access mechanism. The FACOM 462K used a variable length track recording format, and was used with the FACOM 230-60 large computer. The FACOM 462K-1 used a fixed length format, and was used with FACOM 230-25 and 230-35 mid-size computers. The FACOM 462K and the FACOM 462K-1 were the same devices, except for the difference in track recording format.