FP11-C Floating-Point Processor

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The FP11-C was a FPP used in the PDP-11/45 and PDP-11/70 computers (the later KB11-D and KB11-C CPU variants thereof, respectively); it was program compatible with the FP11-B Floating-Point Processor, which was the progenitor of the semi-standard FP11 floating point used in many later PDP-11s.

Like the FP11-B, it operated in parallel with the main processor, so that two instructions (one floating point, one regular) could be processed at the same time; unlike the FP11-B, it used an internal clock which is synchronized to the basic CPU's clock.


It plugged into special pre-wired slots in the CPU's backplane, and included the following boards:

  • M8128 ROM and ROM Control
  • M8129 Exponent and Data Path
  • M8126 Fraction Data Path - High Order
  • M8127 Fraction Data Path - Low Order

Further reading

  • FP11-C floating-point processor user's manual (EK-FP11C-OP-001)

External links