Date   : Mon, 05 Jul 2004 19:22:17 +0100 (BST)
From   : Pete Turnbull <pete@...>
Subject: Re: Acorn Winchester unit

On Jul 5, 10:06, Jules Richardson wrote:

> For starters, did Acorn ever sell Winchester units with SCSI drives?
Or
> were they always ST506 drives with a SCSI-ST506 bridge board
inbetween?

> I think the ACW always used an Adaptec board (ACB400 if I remember
> right), and I have a feeling that's what's in the Winchester unit I
> found too.

IIRC stacking filestores may have had SCSI drives but ordinary
filestores, all Acorn Winchesters, and all ACWs used Adaptec ACB4000s.

> As ST506 drives have no 'get geometry' command, whatever does the
> formatting is going to have to set up the Adaptec board's drive
> parameters somehow. (I have a feeling either the Omti or Xebec boards
> could be configured in ROM, but the Adaptec ones always need it set
up
> in software).

Xebecs do as well, though if you don't initialise them they default to
something like an ST506.  The biggest difference between the Adaptec
and the Xebec in that regard is that the Adaptec controllers store the
config information for the drive (heads, cylinders, etc) on the drive
itself when they format it, and can read it back; the Xebec's have to
be told by the host every time they are reset (not just once for
programming).

> I remember talking to Pete Turnbull about this a while ago (as I was
> after a formatter for my ACW, plus I know he's worked with hooking
hard
> drives up to BBCs in the past. Pete, where are you? :-)

Here ;-)

> Anyway, my point is that your formatting utilities may be making an
> assumption that they're talking to an Adaptec bridge board on the
SCSI
> bus, not a SCSI hard drive. That may well cause trouble and require
you
> to actually format your SCSI drive on a different (non-BBC) machine
> (e.g. use dd on a Unix system).

dd won't change the sector size, though.

> > These
> > programs don't seem to care that my drive is using 512bytes/sector
but
> > as soon as I start to save data on the drives, I run into problemes
> > that invalid data is read from the disk.
>
> Interesting. That implies that the formatter's actually working -
which
> surprises me. Unless it's silently failing :)  (or maybe it's just
> defaulting to assuming you have a 10MB drive attached and only laying
> out the first 10MB of blocks)
>
> Presumably things are getting upset because the host BBC is asking
for
> block n and the drive is sending 512 bytes rather than 256. At the
write
> stage maybe it doesn't matter, as the BBC is probably just saying
"write
> the following 256 bytes to block n" and the drive doesn't care that
> that's not a full block.

I don't know whether that's correct or not, but it sounds plausible to
me.

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York