The Electrical Communication Laboratories (ECL) of Nippon Telegraph and Telephone Public Corporation (now NTT) needed to further improve performance of the DIPS-1 center unit, and as part of that effort, work started on the development of the Model 301 magnetic drum memory unit in 1971. This magnetic drum was designed for use as a high-speed auxiliary memory to fill the access gap between the main memory and magnetic disk memory units. The development goals were high density, high capacity, and higher speed, and it was decided to develop a compact, magnetic drum unit with low power consumption and outstanding economy.
Progress was made in increasing the resolution of the memory media, precision of the floating head, and speed of drum rotation, and in 1977 the Model 301 magnetic drum (JS4160) achieved practical application. It had world-class performance with a recording density of 140 bit/mm, memory capacity of 15 MB, data transfer speed of 11.6 Mbit/s, access time of 5 ms, and rotation speed of 6000 rpm. This Model 301 magnetic drum unit was widely used as a high-speed auxiliary memory unit in banking systems, scientific computation systems, and other systems.