Help collecting gear from west of Chicago

[Eric Smith]

Tony wrote:
> Unibus and Qbus use the same double-sided 36 pin  (18 pin per side) 0.125"
> pitch connectors. Q bus boards are normally dual or quad, Unibus are
> normally quad or hrx.

To be overly pedantic:

Unibus boards are normally dual.  The only real Unibus boards you're likely
to find are the terminators and bus jumpers.  If someone tries to tell you
that a quad or hex board is a Unibus board, they're almost certainly
mistaken, and it is probably really an SPC or MUD/SPC board.  Normally
the only Unibus slots in a PDP-11 backplane are the A-B positions of the
first and last slots, though there are exceptions to that in various
places such as the PDP-11/45 and RH11 backplanes.

SPC ("Small Peripheral Controller") boards are quad or hex.

MUD/SPC ("Modified Unibus Device") boards are hex.

SPC and MUD/SPC boards are commonly but incorrectly called Unibus boards,
but they will not work correctly in a Unibus slot (and technically they
won't even fit).

Extended Unibus slots are found only in the PDP-11/24 and PDP-11/44
processor backplanes and are only used for MS11-M (M8722) and
MS11-P (M8743) memory boards or third-party equivalents.

In some backplanes, one or both Unibus slots (in the first or last
position) are colinear with an SPC slot.  Do NOT try to use a hex
SPC or SPC/MUD board in that slot.

Because PDP-11 systems have quite a variety of different slot assignments,
and even conflicts regarding voltages (15V for core, 12V for semiconductor
memory), people maintaining PDP-11 systems actually need to understand
this stuff.

Eric