Re: CBM-900 floppy disk format/encoding

From: MikeS <>
Date: Fri, 28 Oct 2011 12:09:39 -0400
Message-ID: <B898DA05BC1945D5B8108F2F6D4E304C@vl420mt>
----- Original Message ----- 
From: "Uffe Jakobsen" <>
To: <>
Sent: Friday, October 28, 2011 6:08 AM
Subject: Re: CBM-900 floppy disk format/encoding

> ... I did have time to open up the CBM-900 and had a look inside.
> Also I opened a SFD-1001 just to verify my theory that the CBM-900 uses
> drive that is mechanical identical with the one inside SFD-1001.
> And I was right the drive in the CBM-900 is completely identical with the
> one inside a SFD-1001.
> From that I'll dare to conclude that the CBM-900 floppy disks are
> DS/QD/100 TPI.
> /Uffe
Well, that would seem to settle the question then although the answer to
your original question is effectively the same, i.e. you're using the wrong
type of drive with Kryoflux. Are the drive mechanism model numbers the same
by any chance? It is still remotely possible that they look the same but are
in fact different mechanically/electrically.

But it's more likely that the literature stating that the CBM-900's disks
are 1.2MB capacity was just premature and/or optimistic; then again, perhaps
they really did find a way to squeeze another ~200KB on to a DD diskette. Do
you actually have a running system? If you do, it should be easy to
determine the real capacity.

I think that most if not all of Commodore's LP QD disk drives were made by
Panasonic with custom electronics on a more or less standard mechanism;
if so, perhaps it would be possible to replace the analog board with a
standard interface version from another Panasonic drive which might then be
compatible with a PC and Kryoflux.

Alternatively there are 100TPI drives with a standard interface 'out there'
that might be compatible with a PC and Kryoflux (e.g. Tandon and
Micropolis), but they are relatively rare. I have both 8050s and standard
100TPI drives; if I ever get a Kryoflux or equivalent maybe I'll investigate
some day.

Has anyone ever heard of someone being able to read a Commodore QD
disk on a non-Commodore (i.e. PC-compatible) computer?


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Received on 2011-10-28 17:00:08

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