【Oki Electric Industry】 OKITAC5080, OKITAC5090

The OKITAC5090 was the first machine in Japan to use magnetic core memory for all internal memory. It was completed in 1961, but the OKITAC5080 was developed as a prototype in the previous year. The OKITAC5080 used magnetic core memory for the main memory unit, where almost all Japanese models of the time used magnetic drums, and it was a transistor-based computer which employed a static circuit system. Oki electric industry stopped multiplexing input/output devices and switched to a series system, simplified circuits using the high speed performance of magnetic cores, and there by achieved higher speed and reliability. The results of development of the OKITAC5080 were reflected in the OKITAC5090.

For the OKITAC5090, the A Model was completed first in 1961, and from then until 1963, 6 models were marketed as a series, and became a best-seller for that time. The original A Model used magnetic core memory, and did not use buffer memory at interfaces with input/output devices, so it was possible to connect high-speed input/output devices with good efficiency. Main memory was 4,096 words. Numeric words were decimal, 12 digits/word. Instruction words were the pair-order type with 2 instructions/word. Operation speed was 0.4msec. As input/output devices, the system was equipped with an electric typewriter, a photoelectric paper tape reader, and a high-speed line printer.

The Models A~D became best sellers primarily at Universities, which were a big market at that time. The reasons usually given for this are: high-speed processing using magnetic cores, an easy-to-use instruction set, numerous input/output devices, and especially the fact that a high-speed line printer was connected. In using the magnetic core memory, a great deal was owed to the research results of Toru Motooka of Tokyo University.

OKITAC5080, OKITAC5090 Model Specifications
OKITAC5090 Series
A Model B Model C Model D Model M Model H Model
cement date
1961 May 1961 1962 1963
Control system Built-in program system
Word length 1 word = 42bits 1 word = 50bits 1 word = 42bits
Numerical Decimal,
Sign 1bit + 10
digits + Parity
1bit sign
Sign 1bit + 12
digits +
Parity 1 bit
Decimal, Sign 1bit + 12 digits + Parity 1 bit
Fixed point numbers, Sign 1bit + 48bits + Parity 1bit
Floating point numbers, Sign 1bit + Characte-
ristic 8bits + Mantissa 40bits + Parity 1bit
Only binary
number represe-
Fixed point
numbers, Sign 1bit + 41bits
Floating point numbers, Sign
1bit +
9bits + Mantissa 32bits
Number of instructions 22 52 58 58 64 85 199
Instruction format 2 address system 1 and 1/2 address system,
1 word 2 instructions
Same as at left + Auxiliary word
Index   1, 4 digits 1 15, 1 word length
Operation speed Addition/
subtraction 0.5ms
Multiplication 15ms
Division 17ms
Fixed point number
Addition/subtraction 0.4ms
Multiplication 5.5ms
Division 10.0ms
Floating point number
subtraction 0.7~1.4ms
Multiplication 4.9ms
Division 8.9ms
Fixed point
subtraction 30µs
Floating point
subtractio 85µs
Basic elements Transistors, Diodes
Memory unit Magnetic core
1000 words
Magnetic core
1000 words, 2000 words, 4000 words
Magnetic core
4,000 words, 8,000 words
Magnetic core
8,192 words ~ 16,384 words
Output devices
PTR 2 1 2 1 2 2 2
LP 1 1 1 1 1 2 2
ET 2 1 1 1 1 1 2
CR     1   1 1 2
CP     1   1 1 2
MT       1-6 1-6 1-10 1-45
Other Power consumption
Main unit: 250W
        Magnetic drum (1-10 units) Equipped with magnetic drum and magnetic disk