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IBM 4020 Military Computer

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

Details:

  • 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:

  • 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.

    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.

    References

    IBM 4020 Military Computer Wikipedia