Re: netbsd on vax 11/730; booting in sim

[John Wilson <wilson%dbit.com@localhost>]

From: Johnny Billquist <bqt%softjar.se@localhost>

>The massbus adapter in RM02/03 drives sits beneath the drive, in the 
>same cabinet. I've never played with an RM05, but I believe that one 
>have a larger massbus adapter, that sits on the side of the drive. I 
>also seem to think that two RM05 drives could be paired (I can't 
>remember where I saw that), with the adapter either shared between them, 
>or somehow two adapters could be placed in a shared box between the drives.

It's the second thing -- two separate RM adapters stacked above each other,
with the card cage rotated sideways to fit.  The RM adapter is fundamentally
the same for each of {RM02 RM03 RM05 RM80} but with a slightly different mix
of board revs for each drive type.  So it's not that the one on the RM05 is
bigger, it's that the RM05 drive (I guess I mean CDC 9766?) itself is bigger
(all of the others sit on top of the mini-rack instead of intruding into it)
so there's no space for the RM adapter under it.

Yeah it would have been slick if DEC had made one RM adapter run >1 RM05 drive,
but no.  One of the ways DEC changed SMD was to reverse the direction of the
unit select lines, so instead of the RM adapter selecting a drive depending
on its unit-select plug, the drive is just telling the *adapter* what its
unit-select plug says so the RM adapter knows what its own Massbus unit # is.

John Wilson
D Bit