PDP-11/73 booting!

[Pete Turnbull]

On Dec 12 2005, 16:20, Allison wrote:
> >   From: Pete Turnbull <pete at dunnington.plus.com>

> >All the ones I've ever seen in the field are the same regardless of
> >whther for microPDP-11 or microVAX.  I can't see why the microVAX
one
> >would be different; the microPDP has the CD slots for PMI but the
> >microVAX doesn't care -- it uses over-the-top connections for the
> >memory.
> >
> >The BA23 backplane for a microPDP-11 is an H9278-A and does indeed
have
> >three slots Q22-CD followed by five serpentine Q22-Q22.  That's the
> >same as my microVAX.  And that agrees with the Tech Manuals I have.
>
> Ah, but it doesnt agree with mine. You can use the H9278 for Qbus -11
> but if you want to maximize the slots there was a differnt early
option
> BA23 that had no CD slots(all were AB serpentine) as none of the
> processors before the PMI equipped 11/73 used PMI.  Early
microPDP-11s
> wer really 11/23Bs.  As a result there really were two similar but
> not exactly the same flavors.

OK, but that would be unusual, and not exactly standard :-)   Was that
a protoype?  You could certainly use Q22-CD slots for 11/23-compatible
memory -- yes, I know the microPDP11/23 is just a KDF11-B with
different ROMs -- and I've never seen a BA23 that wasn't 3 x Q22-CD
plus 5 x Q22-Q22, which is what the tech manuals and maintenance
manuals I have describe.  I don't even know of any other 4 x 8
backplane that could fit.

> I know the gory details as my BA23 uVAX
> was hacked from the uPDP-11 and I needed a differnt backplane
> (memory compatability) and the front pannel insert for the drive
> control was different.

Well if you started with a fully-serpentine Q22-Q22 backplane, the
microVAX memory would need it changed, because the cards talk to each
other using the CD-interconnect, which I'd forgotten (but not AFAIK for
CPU/memory transfers, which are over the top).  The front panel,
though, is the same except for the badge, everywhere I've seen.  The
console/SLU panel, the *back* panel, is different, of course.

-- 
Pete						Peter Turnbull
						Network Manager
						University of York