IBM 4020 Military Computer

The IBM 4020 Military Computer[1] was a Cold War era military computer. Two of them were used in the two IBM AN/FSQ-31 SAC Data Processing Systems.

Details:[1]

* Instruction rate : Up to 400,000 instructions per second
* Cycle time : 2.5 microseconds
* Word size : 48 bits + 2 parity bits
* Core storage : up to 131,072 words
* operates in parallel mode
* 69 instructions
* single address instructions
* Add or subtract : 2.5 microseconds (fixed point)
* Add or subtract : 7.7 to 26 μs (floating point)
* Multiply : average 24 μs (24 bit precision fixed point)
* Multiply : 5 to 74 μs (floating point)
* Multiprocessing with Automatic Priority

The instruction format includes:[1]

* 7 bit op code
* 2 bit real data indicator
* 3 bit byte displacement
* 3 bit mode selector
* 1 sign bit
* 8 bit 'byte activity'
* 1 bit Double index flag
* 1 bit Indirect address flag
* 4 bit index register selection
* 18 bit address.

Man-machine communications included a light-gun to indicate an area of interest on a visual display unit.[1]

Circuit logic packaging was based on 7 types of Q-pacs each holding 1 to 4 circuits. Transistors and semiconductor diodes were soldered to the outside of the Q-pac encapsulation for ease of cooling and replacement.[1]

## References

[edit]

1. ^ a b c d e The IBM 4020 Military Computer - General Information (PDF). IBM Federal Systems Division. October 31, 1959.

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