An NEC research laboratory in 1961 set out the development concept for the NEAC-L2, an ultra-high-speed, large-scale computer that was the focus of a multiyear base research project. Development was divided into three phases. In the first phase, the central unit was developed, after which memory capacity and peripheral devices were expanded and improved. The first phase was completed in June 1964. Kobayashi Ryo invented the high-speed current-switching circuitry for the core circuits, which were the heart of the computer. With this innovation and Ge transistors, a clock frequency of 30 MHz was obtained. The NEAC-L2 was hailed at the time for its cutting-edge acceleration techniques and hardware. Some examples of these are listed below:

  • Simultaneous processing of multiple instructions
  • Interlacing for higher memory-unit performance
  • Multiprogramming
  • Method for program interrupts
  • 10 MHz, two-phase core logic circuits
  • 40-bit, 100 ns adde
  • 100 ns tunnel-diode memory units (used as registers)
  • Magnetic core memory with non-destructive reads and a 1μs cycle time (used as main memory)

This project produced a large amount of valuable data and experience, which proved useful in later large-scale computer development.

Specifications of the NEAC-L2
Completed June 1964
Computation method Binary, fixed-point and floating-point calculations
Logic elements ~16,000 transistors, ~50,000 diodes
Word structure 36-bit binary words
Fixed-point values: sign + 35-bits
Floating-point values: sign + 7-bit exponent + 28-bit coefficient
Instructions 1 1/2 addressing system 140 instructions
Computation speeds
  Fixed-point Floating-point
Addition and subtractio 0.5〜2μs 1.4〜2.6μs
Multiplication 1.9〜7.7μs 2.4〜7.0μs
Division 11.4μs 9.8μs
Memory units (magnetic core)
8,192 words, cycle times : read : 1μs , write : 2μs

ROM: 1,024 words, cycle time : 0.5μs
Index registers 15, using tunnel diodes with a 50 ns access time
Magnetic disk unit 50 Mbits, average access time: 250 ms, 90,000 characters/s
Magnetic tape unit Tape speed: 4 m/s, recording density: 10 bits/mm, eight units 80,000 characters/s
Line printer 120 characters/line, 96-character set, 300 lines/minute, one unit
Photo tape readers Read speeds: 200 characters/s and 1,000 characters/s, one unit each
Paper-tape punch writer Print speed: 500 characters/minute
Punch speed: 700 characters/minute Five units
Power consumption ~20 kVA

NEC NEAC-L2NEC NEAC-L2’s transistor circuit board