On Thu, 8 Jan 1998, John Wilson wrote:

> >From: mxs46@po.CWRU.Edu (Michael Sokolov)
> 
> >   What I don't quite understand is why do they use unit plugs in the first
> >place. SDI uses purely radial connections for multiple drives, and each
> >drive connects to a different port on the controller. On all machines with
> >RAxx disks that I have seen (only two really :-)), there was a perfect
> >match between the number of the port on the controller and the number on
> >the unit plug on the drive. Does anyone have a clue as to what's going on?
> 
> The docs encourage Field Service to install it that way so it's no surprise
> that drive 0 is usually on port 0 etc.  However the MSCP spec requires that
> unit numbers be unique on the *system*, not just within the controller;  so
> once you add the second MSCP controller the port-unit matchups stop working.
> Seems like an annoying rule though, all other types of disk/tape units only
> have to be unique within the controller.

Well, I can tell you that it really isn't mandatory. I've run a 8650 with
Unix, four UDA-50s and all disks had unit numbers between 0-3, but I
kindof realized that it was a big pain, since it was hard to remember
which disk was which... :-)

	Johnny

Johnny Billquist                  || "I'm on a bus
                                  ||  on a psychedelic trip
email: bqt@update.uu.se           ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol