MS11 Semiconductor Memory System

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The MS11 Semiconductor Memory Systems were a set of special high-speed memories for the PDP-11/45, which plugged into special dedicated, pre-wired slots in the backplane of the the KB11-A and KB11-D CPU.

The MS11 was dual-ported memory, with one port connected to the separate 'B' UNIBUS of the PDP-11/45, and the other to the CPU through a special bus, the Fastbus. A PDP-11/45 could have up to two separate MS11 banks.

There were three different versions: initially the MS11-B MOS (450 nsec) and MS11-C bipolar memory (300 nsec); and later the MS11-A larger, but otherwise identical, bipolar memory.

Any version could be added to a stock PDP-11/45, but DEC sold versions of that machine pre-configured with MOS or bipolar as the PDP-11/50 and PDP-11/55, respectively.

In all versions, each bank included a controller board, and up to 4 storage boards; all cards were hex size. Each bank had to be all MOS or all bipolar (one size); however, there could be one bipolar bank and one MOS bank.

The storage boards were available in both non-parity and parity versions (except the larger bipolar ones, which were available in parity only), the latter being indicated by a trailing '-YA' on the board number.


The MS11-B consisted of:

  • MS11-BC or -BD MOS Memory Control (M8110)
  • MS11-BM, -BP, -BR and -BT 4K MOS Memory Matrix (G401)

In addition, the MS11-B required the special H746 MOS Regulator power supply module, which produced the special voltages needed by this memory.

The -BC and -BD variants are DEC nomenclature for the first and second controllers, both being packaged with an H746, but only the former also included the needed extra H744. The -BM and -BP are the nomenclature for the non-parity and parity versions.

MS11-C Bipolar

The MS11-C consisted of:

  • MS11-CC Bipolar Memory Control (M8110)
  • MS11-CM, -CP 1K Bipolar Memory Matrix (M8111)

The M8110 was later replaced by the M8120, which used the same printed circuit board, but with (as yet un-determined) component variations. The -CM and -CP are the nomenclature for the non-parity and parity versions.

MS11-A Bipolar

The MS11-A consisted of:

  • MS11-CC Bipolar Memory Control (M8120)
  • MS11-AP 4K Bipolar Memory Matrix (M8121)