Date : Tue, 23 Mar 2010 19:34:03 +0000
From : beeb@... (Dr. David Alan Gilbert)
Subject: Re-using floppies
* Anders Carlsson (anders.carlsson@...) wrote:
> Phill Harvey-Smith wrote:
>
> > But arn't 35 and 77 track drives just 40 and 80 track drives
>
> Lately I've come to learn about the Commodore 8050 and 8250 drives.
> Those use Tandon, Micropolis and Matsushita mechanisms and format
> a disk to 77 tracks = about 500 kB per side! :-o All the experts
> keep saying you are supposed to use the quite uncommon 100 tpi DD
> floppy disks, rather than the more usual 96 tpi DD (QD) ones.
Woah! That's the 2nd time I've seen reference to 100 tpi discs - can
you give some more information?
The Commodore drives to my knowledge were VERY odd; they used
special mechanisms and had a hell of a lot of processing in them (and HPIB
or similar out the back - one I picked up 2nd hand had a 6502 and 6510
(from memory) and a fairly useful haul of 6532s and other 65xx chips).
However, what really interests me is that I got a pair of 100tpi Teak
drives many years ago (full height, 5.25") by accident in a junk
sale (we were lucking for a pair of 80 track drives for our Model B!).
Those Teak drives have standard Shugart interfaces (and were in a nice
external box) - but if Commodore drives always had special interfaces,
I'd love to know what else used 100tpi ?
> I have tried to understand why. A blank floppy disk should not have
> any fixed grooves, so it should be able to lay out any number of
> tracks less than the certified maximum? Perhaps it is a matter that
> a 100 tpi floppy disk will be more reliable to reformat 77 tracks
> than a 96 tpi one.
My guess is that things get messy when you reformat the discs if
they've been formatted at one stepping and end up with tracks sitting
partly overlapping where your new tracks are but which don't properly
get erased - just a guess.
Dave
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