DSQD Drives (Was: RE: Diags/Boot image for Altos 580)

From: Fred Cisin <cisin_at_xenosoft.com>
Date: Sun Mar 17 19:27:30 2002

On Mon, 18 Mar 2002, Tony Duell wrote:
> Does any 1.2Mbyte drive do double stepping in hardware?
Not that I've ever seen.

> I've never seen
> one that does (in fact most 'double stepping' drives have been modified,
> they were not designed like that). And I've just checked the PC/AT BIOS
> sources, and that machine most definitely double steps in software when
> reading a 360K (40 cylinder) disk in a 1.2M (80 cylinder) drive.

The problem may be occurring (if it exists at all) from programmers trying
to interface with the existing software at too high a level.
One of my "colleagues" (competitors) was trying to do some stuff with DEC
diskettes and reported having problems with it. I never saw his source
code, but since he was trying for emulation with maximum OS transparency,
I'm going to guess that he was trying to use the MS-DOS API "raw
read"/"raw write" routines.

I also got two reports from users of getting (#64) "seek error"s when
trying to read Eagle diskettes in what they said were 1.2M drives. Those
users were unable to provide coherent followup, and had no problems once I
talked them through temporarily installing one of the Eagle drives (QD).

Fred Cisin                      cisin_at_xenosoft.com
XenoSoft                        http://www.xenosoft.com
Received on Sun Mar 17 2002 - 19:27:30 GMT

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