Re: Did Commodore cheat with the quad density floppies?

Den Fri, 4 Jan 2019 22:08:33 +0100 skrev Francesco Messineo
<francesco.messineo@gmail.com>:
> I guess (and it seems reasonable) that CBM engineers used the highest
> amount of bytes per tracks in the various zones that allowed reliable
> (by a large margin I'd say) operations. I can still read most of the
> disks that were last written around 1989 or so.
> If we agree that they found the optimal sector per tracks in the
> various zone by probably experimenting (and the 2040/4040 format
> difference seem to suggest that), then I don't see why the same
> engineers would not try the same method using the 100 tpi mechanics:
> see what they can do, maybe tweak a bit the head write current and/or
> pulse shape and see what can be reliably done on the same 300 oersted
> magnetic media, just with better mechanics and smaller heads.
> I never had the luck to have a 100 tpi drive, so I don't know if the
> disks written around 198x are still readable nowadays, but if the
> failed disks have the same percentage of the ones written with 48 tpi
> mechanics, then probably the reliability of the write format was as
> solid as the one used on 48 tpi drives. If, on the other hand, 100
> tpi-written disks are much less readable (and by a large amount, I'd
> say) then we could conclude that CBM engineers went too far pushing
> the limits of the 300 oersted media and the 100 tpi mechanics
> combination.

IIRC the low profile 100 TPI drive Commodore did use were also
available as a 96 TPI HD "PC" drive. So it seems likely that the heads
were small enough to make a higher data rate possible. I doubt that the
drive manufacturer actually made special heads for Commodore, or for
that sake used some older kind of heads that wouldn't work with the HD
format on a PC.

I doubt that the heads are square, as you only have 35-80 tracks in one
direction (depending on drive type) while you have several kilobytes in
one turn of the drive, which probably equals to a data depth difference
of about 1:1000 when comparing the two directions on a drive head.


BTW before IBM AT and it's HD format, it seems like the idea with 96TPI
drives were to use 8" formats on 5.25" media. That way they could be
used without any adaption of existing operating systems. In ads I've
seen in magazines from mid 80's the TEAC 96 TPI drives were sold as 77
track and not 80 track drives. Of course 80 tracks did actually work
fine on them.


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