16 May
2025
16 May
'25
10:57 p.m.
On Friday, May 16, 2025 at 12:13:30 PM PDT, John H. Reinhardt via cctalk
<cctalk(a)classiccmp.org> wrote:
They are hybrid - BA23 has slots 1-3 as Q22/CD and
then 4-8 are Q22/Q22
I believe the BA123 is Slots 1-4 Q22/CD and 4-12 are Q22/Q22
BA123 has 4 Q22/CD slots and the rest are Q22/Q22. There is another slot behind, slightly
raised, which is 'reserved'. I believe the dual height RQDX3-Extender cards are
permitted in the "raised" slot, but I'd have to check which half.
BA213 and 215 are Q22/CD entirely.
Several of the Q18 backplanes can be converted to Q22 by modifying or wire-wrapping the
four pins. The path is serpentine -- alternating left-to-right/right-to-left by row.
frainresearch.org had instructions and pictures, and useful information on Qbus
termination. That site is gone, but the content is still on the Internet Archive's
WayBack machine:
https://web.archive.org/web/20150506140342/http://web.frainresearch.org:808….
However a pure Q22/Q22 backplane will not support any Microvax II or III memory cards, as
they use CD slots as part of the Private Memory Interconnect (PMI) to the CPU. You could
run a KA630 with just the 1MB on the CPU board; but it'd be even more constrained than
a microvax 2000/vaxstation 2000 with just the 2MB onboard memory.