Plessy core memory

[Noel Chiappa]

    > From: Chris Zach

    > the secondary memory (a Plessy 700101-100) may be shorting the -15 line
    > for some reason. Working on it, but does anyone have a manual or
    > anything like that for this kind of memory board?

I've got a Plessey core memory manual somewhere, but I can't find it, so I
don't know if it's the one you are looking for. I got it from Paul Birkel; it
was a duplicate, and he scanned his and sent the scan off, but I don't think
it made it online.


    > Alternately, what kind of Unibus 16k memory board exists to get a 11/10
    > from 16kw to 32kw of memory?

It all depends on what kind of -11/10 you have.

If yours is in a 5-1/4" box, you can't plug a DEC memory card into the SPC
slots that some of the CPU-holding backplane versions have because DEC
memories (other than the ones like the MM11-L and -U, which are multi-board
core systems that require custom backplanes) all require MUD slots, not SPC.

All of the CPU backplanes on that machine are for a _specific_ kind of core
memory (MM11-L or MM11-U), see here:

  https://gunkies.org/wiki/PDP-11/05

There are I think some third-party memories which can be used (Dataram,
maybe?) but I don't have time to go into them.

If you have a 10-1/2" box, you can mount a MUD backplane - but you might
still have an issue because the older BA11-D boxes use the old 9-pin power
connectors, and the MUD backplanes (DD11-C, -D, etc) all use the newer 15-pin
ones.

(Again, there are some oddball ones, and again, I don't have time to go into
them.)

If you're lucky enough to have one of the ones that will take a MUD backplane,
an MS11-E/F/H/J:

  https://gunkies.org/wiki/MS11_32KB_MOS_memory

would be an option.


  > On a related note, where did +20 come from for Unibus and which systems
  > even supported it? Was it an 11/45,11/70 thing?

The later /05's, /40's and /45's were the first ones to provide +20V, for the
then-new MM11-U. On machines which took H744 'brick's, the _later_ harnesses
could take a H754 +20V, -5V regulator 'brick'. Alternatively, _some_ BA11-L's
(used for the /04 and /34) had the right version of H777:

  https://gunkies.org/wiki/H777_Power_Supply

to provide +20V.

	Noel