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The LSI-11 was DEC's first cost-reduced PDP-11 CPU, using the QBUS and the LSI-11 chip set. They were popular in OEM usage.

The LSI-11 is a quad board (M7264) with additional functionality on-board. (A later board, the LSI-11/2, packaged just the CPU on a dual card.)

The LSI-11 is a Q16 device; it only drives 16 address lines. Although it can be plugged into a Q18 or Q22 backplane, it will only function with Q16 main memory. (With Q22 memory, the pins used for BDAL18-21 are used for other, internal signals by the LSI-11. The reason for the incompatability with Q18 memory is currently unknown.)

The usual CPU options were available for the LSI-11: the KEV11-A, for the EIS/FIS instructions; the KEV11-B provides EIS without FIS; the KEV11-C provides a subset of the PDP-11 CIS (it also apparently includes the EIS, but not the FIS).

It also supported the optional KUV11 Writeable Control Store.

The chip order (from the left, with the contact finger edge down, and the component side facing the viewer) is KEV11, uROM 1, uROM 0, Control, Data Path.

Variant models

Many different LSI-11 models exist, including the KD11-F and KD11-H base versions, and numerous other variants. The KD11-F version includes 4KW of MOS RAM on-board; the KD11-H version has the RAM deleted.

Others included various KEV11 chips pre-installed:

  • the KD11-L is a KD11-F with a KEV11-A
  • the KD11-N is a KD11-H with a KEV11-A
  • the KD11-P is a KD11-F with a KEV11-C
  • the KD11-Q is a KD11-H with a KEV11-C

Some models include additional cards: