> > Also, on all but one of the processors, they'd be paying a speed
> > penalty, and from what I recall a fairly hefty one.
> 
>    Yes...Qbus tops out at 3.3MB/s if memory serves, then there's any
> latency incurred by the arbitration logic on the CPU. :-(

when acting as a memory server between the pmmi and the qbus, a ka630
or ka65* series box operates in block mode (acts like a dma device).
you should be able to get the full 30Mbit/sec out of it.

many of these ideas got completed and extended and used in the later
"firefly" (at dec src) and "firefox" (name of the 3520/3540 product
version of the dec src box).  for example, more than one cpu per pmmi.

a 3540 with full memory, plus a three-board qdss, plus a 2-board qda50,
was a *monster* with ribbon cables up and down the card stack.  noisy!
power hungry, too -- i used one to justify dual 20A breakers per desk
in a new dec office building once upon a time.