Date   : Tue, 23 Mar 2010 20:14:43 +0100
From   : anders.carlsson@... (Anders Carlsson)
Subject: Re-using floppies

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.

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.

> Then there's flippy disks which have two sync holes so you can flip
> them over, I seem to remeber these being used on the Commodore PET.

Well, don't you need a second sync hole (in the jacket) to use
flippies with a single sided drive on the BBC Micro too?

I am not sure if any of the 35 track drives (2040, 3040, 4040, 2031)
use the sync hole, but I suppose you need a second sync hole to flip
a disk in the 8050.

Speaking of which, does anyone know a tool or method to safely punch
a second sync hole into a floppy disk jacket? I suppose one can take
measures and cut something by chance, but how to cut open a hole
without damaging the disk inside?

Best regards

-- 
Anders Carlsson