For DIPS-1, magnetic core memory was used for the main memory units, but it was extremely expensive at that time -- accounting for approx. 30% of the host-center system-hardware cost. There was a need for high-capacity, high-speed virtual memory, and magnetic drum memory units were used for that.
In response to the demand for high performance DIPS-1 center systems, the Electrical Communication Laboratories (ECL) of Nippon Telegraph and Telephone Public Corporation (now NTT) developed the magnetic drum memory unit No. 1 by adopting the floating head technology unit in 1970, which was used as a virtual memory unit for swapping out. They achieved a comparatively high-speed average access time (10 ms or lower) and high information-transfer speed. This No. 1 magnetic drum memory unit had a memory capacity of 4 MB, information recording density of 56 bit/mm, rotation speed of 3000 rpm, average access time of 10 ms, and information transfer rate of 2.2 MB/s.
No. 1 Magnetic Drum Unit (Unit capacity 4 MB)