DEC PDP-11/10

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I have two PDP-11/10 units.

The first one has been upgraded to MOS memory before I received it.

The second one still uses core memory.

Both are in working order (or at least they were in working order when I last tested them).

PDP-11/10 with MOS memory

This is a very bare-bones system.

It has 3 backplanes (9-slot, 9-slot and 4-slot). The second backplane holds a hex-height MOS memory board. I was told this machine uses a “Modified UNIBUS backplane”. I am not sure whether this affects all 3 backplanes, or just the second one. Care needs to be taken here.

The backplanes are fitted with the following cards (excluding M920 UNIBUS connectors and grant continuity cards):

Backplane 1:

  • Slot 1: AB = empty. CD = M9970. EF=Empty
  • Slot 2: AF = M7260
  • Slot 3: AF = M7261
  • SLot 4: AB = M930 (terminator?). CF = Empty
  • Slot 5-9: Empty

Backplane 2:

  • Slot 4: Plessey P/N 701295-???F (128KW MOS Memory board)
  • Slot 6: M7867 (synchronous modem interface)

Unfortunately the suffix on the part number for the Plessey MOS Memory board is unreadable. The board is fitted with 4 rows of 18 x 4116 dynamic RAM chips. I guess this means it has 64KW of parity RAM. That’s a bit surprising, given that the PDP-11/10 only has a 16-bit address space. I need to investigate this further. It has one 10-way dipswitch on the board. Switches 1-7 and 9 are ON. Switches 8 & 10 are OFF.

The DUP11 is a synchronous modem interface. It operates under various protocols (SDLC, ADCCP, DDCMP, etc). The User’s Manual for the DUP11 is available on bitsavers here ->

Some grant continuity cards are fitted, but many appear to be missing. There is no terminator at the end of the final (third) backplane.