Re: SCSI expert needed

From: Ethan Dicks <>
Date: Thu, 27 Jan 2011 09:54:04 -0500
Message-ID: <>
On Thu, Jan 27, 2011 at 9:34 AM, Anders Carlsson
<> wrote:
> Peter Krefting wrote:
>>> Also in this case the DC "knows" it deals with a 5 or 7.5 MB hard disk.
>>> For example, the number of sectors/track is hard coded to 20.

$20 - 32 sectors of 256 bytes (the "standard" PC formatting of the day
was 17 sectors of 512 bytes)

>> That helps. It also makes it harder to replace the disk later...

Without changing the ROMs, yes, but the code for that was sleuthed out
some time ago - there's one I/O bit that's used to determine 4 heads
vs 6 heads.  The rest of the parameters are in a table in ROM (or
coded as constants).

> Fortunately in this case, the 5 MB Tandon 602S found in a D9060 is to most
> part possible to replace with a 20 MB (?) Seagate ST-225.

21.4MB technically, but, yes, 20MB (615 cylinders, 4 heads, 17 sectors
of 512 bytes or 32 sectors of 256 bytes)

> However due to the
> hard coded addressing, only 1/4 of the latter disk will be in use. I think

Yes.  The requests won't go past the number of cylinders in the
TM602S, so 75% of the surfaces go unused.

> the same holds true for the 7.5 MB Tandon 603S but it requires a ST-231 or
> such.

Yes, the ST-251 (nominally 40MB).  There are two versions, the ST251
uses a stepper motor with a seek time of 65ms (same as ST225), and the
ST-251-1 which uses a voice coil and has a faster seek time (40ms?
25ms?) but is otherwise equivalent.

> Actually one of the persons who had expressed an interest in a D9060 decided
> to not buy it from me when I announced it contained a ST-225 rather than the
> original Tandon drive. I suppose it is important if you want it for your
> collection and not so much for using it.

There are folks on both sides of that - some want an original
artifact, others just want a working drive and don't care what's in
the box.


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Received on 2011-01-27 15:00:31

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