SENAC-1（NEAC-1102）

SENAC-1 (NEAC-1102) is a practical parametron computer produced at the age of early computers　in Japan. A need arose for a high-performance computer for scientific and engineering calculation, capable of highly accurate arithmetic operation at the Research Institute of Electrical Communication Tohoku University and NEC Corporation (NEC), and the joint development of a large-scale computer by both organizations started in 1956 under the leadership of Juurou Oizumi of the Institute. This computer was named SENAC-1 (Sendai Automatic Computer 1) after the name of a place of Sendai where Tohoku University is located. It was called NEAC-1102 by NEC, and became the first commercial computer shipped by NEC.

Using about 9,600 parametrons, NEAC-1102 realized a high precision arithmetic operation by adopting the word length of 48 binary digits (bits) , and manipulating double-length calculations easily by two sets of accumulators and adders. It achieved the switching by an instruction between a fixed point arithmetic mode and a floating point arithmetic mode, and aimed at a highly accurate scientific arithmetic operation. The internal memory of 1,024 words was achieved with a high-speed magnetic drum, and the design concept of the adoption of the index modification with five index registers and the look ahead control methods etc. was extremely novel at that time.

The SENAC-1 was delivered to Tohoku University in March, 1958, and started operation in November of the same year. It was used in a lot of region of research of Tohoku University until 1965, and it greatly contributed to the research development.