MSV11-D/E MOS memory

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M8044 memory card

The MSV11-D (M8044) was a dual-height QBUS DRAM main memory card; the MSV11-E (M8045) is identical (apparently even using the same etch PCB), but adds byte parity. They were used in the LSI-11 PDP-11.

They held 64KB when fully populated with 16Kx1 DRAM chips. Initially they used 4Kx1 DRAMs, giving 16KB when fully populated; later/larger ones used 16Kx1 DRAMs. The memory is arranged as 2 banks, each 16 data bits (one PDP-11 word) wide, optionally with 2 additional bits for parity (1 per byte) in the MSV11-E. Half-populating them (i.e. 1 bank only) produced 8KB and 32KB sized versions (depending on DRAM type).

Four versions of the parity/non-parity types exist:

  • MSV11-DA, -EA - 8KB (4K DRAMs)
  • MSV11-DB, -EB - 16KB (4K DRAMs)
  • MSV11-DC, -EC - 32KB (16K DRAMs)
  • MSV11-DD, -ED - 64KB (16K DRAMs)

Note that, in common with many DEC boards, the model variant is not the same as the board variant; there is a 'shift' operation when going from one to the other. All MSV11-D cards are 'M8044-xy', where 'x' is not (necessarily) 'D'; all MSV11-E cards are 'M8045-xy', where 'x' is not (necessarily) 'E'. So the MSV11-DC is tagged 'M8044-Cx' (where 'x' varies, depending on the source of the DRAM chips used).

All are Q18 (hence, could not be used in Q22 systems, such as PDP-11/23's with more than 256KB of memory). They had internal memory refresh.


Note that "M8045" and "32K 18 BIT MOS MEM" is shown in the etch of the PCB used in both the M8044 and M8045; this occasionally leads to them being mis-identified. A quick glance at the board in question will show whether the middle column of DRAM chips (used for parity) is present (notice they are missing, in the image above, of an M8044), and whether it is half or fully populated.

Also, a card tagged "M8044-EH" has been seen; this is probably the result of a production error. An "M8044-EH" implies it is an MSV11-DE - which does not exist. An "M8044-EB" has also been reported.

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