I'm not sure that there was, in fact, a "common command set" as was intended for
SCSI. A specification for matching drive and controller capabilities is
advisable.
In the PC environment, there was considerable variation in the controllers'
capabilities. The WD controllers, WD1005, and WD1007 seemed to have half-baked
abilities to translate tracks to what would fit in the old WD1003-WAH model, but
since most ESDI drives had LOTS of cylinders, in some cases over 4000, it was
not done on those series of controllers. I understand from someone who stuck
with ESDI longer than I, that the WD1009-series was capable of dealing with
that.
I once had a Lark Associates controller that exhausted all the head/sector
number translation options, and, having done that, split the drive in to two
logical drives, then lied to the system and told it that it had two PHYSICAL
drives. That was clever! It was the only way to get the Maxtor and Miniscribe
drives I had, with >750 MB capacity to work on a PC, and it did that quite well.
Unfortunately, the controller caught fire one day ... <sigh> ... so I gave the
larger ESDI drives I had away.
Dick
----- Original Message -----
From: "Tony Duell" <ard_at_p850ug1.demon.co.uk>
To: <classiccmp_at_classiccmp.org>
Sent: Sunday, April 08, 2001 12:15 PM
Subject: Re: ESDI drives
> > >
> > > No, it's a pretty low-level interface, like ST506/412. I read somewhere
> > > that it was designed as an enhanced/faster ST412 interface, possibly by
> > > Maxtor and Miniscribe, and I think Maxtor used to have some information on
> > > their website. All I can find now, though, is a line in their glossary.
> > >
> > It's not low-level in the sense in which ST506/412 works, in that the drive
> > doesn't rely on the controller to modulate/demodulate the data stream, nor
does
> > it rely on the controller to micro-control the head positioning. It
responds to
> > high-level commands, e.g. "format the track" and executes them as determined
by
> > drive-resident firmware rather than a controller-determined protocol, more
or
> > less as does the SCSI, though it doesn't buffer the data and it doesn't do
its
> > own error correction. Though the transfer rates are pretty high, because
the
> > controller does so much of the work, and because raw data rather than
processed
> > data flows between drive and controller, parallelism between drives is not
> > possible.
>
> Yes, that's what I thought. It's a bit like SMD or the interface on a
> Micropolis 1200. In that the data is transfered 'raw' (so the controller
> has to decode the bitstream, do error detection/correction, etc) but
> things like head movement are done at a higher level than 'step one track
> towards the spindle'.
>
> I guess what I meant by a 'spec' is :
>
> Pinouts
> Signal descriptions
> How to send commands/read status
> What the commands are.
>
> -tony
>
>
Received on Sun Apr 08 2001 - 14:11:00 BST