PDP-11/84 Qbus slots for memory

Noel Chiappa jnc at mercury.lcs.mit.edu
Sun Jul 22 12:54:25 CDT 2018

    > From: Mark Matlock

    > With the 11/83 the position of the memory board ... above the CPU uses
    > PMI

Yes, through the C-D interconnect; described in detail here:


The 'above' is because the CD interconnect is not a true bus, it only
interconnected pairs of slots.

    > In the 11/84 the CPU is above the MSV11-JE memory

The PMI is still on the CD connector in this machine, but the PMI is wired as
a true bus on the backplane, allowing that ordering.

    > there are 3 Bus slots in the 11/84 above the Unibus map board, would it
    > be possible to put a dual width Q22 I/O board in the second memory slot
    > (not the PMI side of the slot) and have it able to DMA into the
    > MSV11-JE? 

It is speculated that this should be possible, but there are jumpers on the
backplane you'd need to pull. See the writeup here:



More information about the cctech mailing list