KE11-A Extended Arithmetic Element

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The KE11-A Extended Arithmetic Element is an autonomous UNIBUS peripheral which can perform a variety of arithmetic or logical operations:

  • multiplication
  • division
  • multi-bit shifts
    • logical shift
    • arithmetic shift
    • normalization

(The last is used for implementation of floating point in software.)

It is implemented as a four-slot system unit (details below).

The KE11-A was originally produced for use with the PDP-11/20, whose KA11 CPU did not have multply, divide, or multi-bit shift operations. As a UNIBUS peripheral, not integrated into the CPU, it was also usable with other models, e.g. the PDP-11/05 and PDP-11/04, which likewise did not implement multiplication in hardware, etc.

The KE11-A can be operated with an optional KM11-A Maintenance Set in order to diagnose faults.


The KE11-A consists of 3 quad boards:

  • M7210 Data Control
  • M7211 Register Control
  • M827 Clock and States

and a pair of M234 Register dual-height boards, plugged into a quad backplane.

Board locations

These are the board locations for the KE11-A (as seen from the board side of the backplane):

Slot A B C D E F
1 UNIBUS In M7210 Data Control
2 Unused KM11-A M234 Register
(low byte)
M234 Register
(high byte)
3 G772
Reserved M7211 Register Control
4 UNIBUS Out M827 Clock & States