【Tohoku University,NEC】 SENAC-1 (NEAC-1102)

At the Tohoku University Research Institute of Electrical Communication and within NEC, a need arose for a high-performance computer for scientific and engineering calculation, capable of high-precision arithmetic, and joint development of a large electronic computer by the two organizations began in 1956. This computer was named the SENAC (Sendai Automatic Computer) after the city of Sendai, where Tohoku University is located. At NEC, this was a parametron based computer called the NEAC-1102, and it had the following features:

  • It achieved a high-capacity memory of 1,024 words using a magnetic drum.
  • Switching between fixed point arithmetic mode and floating point arithmetic mode could be done with an instruction.
  • Word length was 48 digit (bit) binary, so arithmetic precision was high.
  • It had two accumulator and add circuits, and could easily perform double-length calculations.
  • Instruction length was 24 digits, and 2 instructions could be held in one word.
  • Index modification could be done using 5 index registers.
  • It employed a look-ahead control system.

The SENAC-1 used approximately 9,600 parametrons. It was manufactured by NEC, delivered to Tohoku University in March 1958, and went into full-scale operation in November of that year. This machine was the first electronic computer shipped by NEC.

SENAC-1 Specifications
Completion date November 1958
Control system Stored program system
External numeric word Decimal, sign + 12 digits, characteristic ±38
Internal numeric word Binary 48 digits (bits)
 Mantissa: 39 digits + sign
 Characteristic: 8 digits
Commands (Instructions) 1•1/2 address system, 29 types
Arithmetic system Parallel, floating point and fixed point
Operation speed Addition/Subtraction: Average 1.4ms (0.3ms)
Multiplication: Average 1.2ms (1.2ms)
Division: Average 10ms (10ms)
The value in parentheses is for fixed point.
Arithmetic element Number of parametrons: Approx. 9,600
 Drive frequency: 2MHz
 off-and-on frequency: 19.5kHz
Internal memory unit Magnetic drum: 1,024 words
Input/Output unit Tape reader: 600 char/min
Tape punch typewriter: 400char/min (printing)
 600 char/min (punching)