FACOM 856 Magnetic Disk Unit

The FACOM 856 magnetic tape unit was the type with movable disk access head, and was developed as an auxiliary memory device for the FACOM 241D computer. This unit was comprised of a magnetic disk controller and a maximum of 4 connectable magnetic disk mechanisms, and memory capacity was 4.8–19.2 million words (40bit/word). The magnetic disk was comprised of 16 disk plates for information memory, 1 plate for clock, and 1 plate for baffle. There were positioners for each of the 16 information memory disk plates, and 8 access heads were attached to each positioner arm. Average access time was 195ms (at 50Hz). This equipment was connected to main memory of the FACOM 241D via the data channel of the FACOM 241D, just like a magnetic tape unit.