On Mon, 8 May 2000, Marc Schneiders wrote:

[snip]

> There are two controllers (at least): One has DILOG on the blue 
> plastic thing with which you can take it out. This is similar to the
> brown plastic handle on DEC cards (like the M7555, which I just
> learned is the RQDX3 controller).
> This is a SCSI controller with 50 pins connector. I took it out. It
> has a NCR 53C90A on it. This only has an Exabye tape connected to
> it. Machine will not get through NetBSD boot without it. Hangs at 
> 
> uba0 at ibus0: Q 22.
> 
> Do I have to tell the machine in the boot monitor that it isn't
> there?

Actually, qbus requires something called a "grant continuity card."  This
basically jumps some wires from one side of the bus to another, allowing
the bus to function as an uninterupted chain.  With qbus, the bus is sort
of a chain - each card has to jump certain lines to the next card; thus
when you remove a card, the cards down the line get [partially] "cut
out" of the chain (hence grant _continuity_ :).

You could shuffle the cards down by one, but that can prove troublesome
unless you know what's going on.  I've got two 4000/200s at home which I
fire up from time to time, and although I've been able to swap cards
around pretty much willy nilly, there can be troubles.  From what I
hear, knowing the incantations which allows a person to move cards around
and put them in the right order is what differentiates the assistants from
the wizards of the vaxen universe ;-)

If you're new to qbus, http://www.telnet.hu/hamster/dr/qbus.html has some
good priming info on the what, where, why and how of qbus.  There's also
bunches of random interresting bits at http://www.vaxarchive.org

[snip]

> The funny thing is that there is another card that seems to be a disk
> controller (number 3). This has no name on it (as far as I can see),
> but it does have the brown plastic handles. It connects to the M7555.
> In fact it is the only thing connected to the M7555. The card itself
> is connected with a cable ("Spitfire-Strip") that goes inside
> somewhere and that connects probably to the floppy drives. Thus:

Just a tidbit of trivia - the "spitfire" is the name of the 4000/200s.

-Jon
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 "There is no fourth tower of Inverness!!!" -Meatball Fulton