Date   : Tue, 23 Mar 2010 12:02:08 -0500
From   : jules.richardson99@... (Jules Richardson)
Subject: Re-using floppies

Pete Turnbull wrote:
> On 23/03/2010 00:01, J.G.Harston wrote:
> 
>> Don't get 5.25" DD/HD mixed up with 3.5" DD/HD. The magnetic
>> coercitivity of 5.25" disks between DD and HD is something like
>> double, whereas with 3.5" it's about 20%
> 
> 25% to 30% actually.  And that's certainly enough to make the abused 
> disks unreliable.
> 

Yes, my brain's saying 3.5" DD was 600 oersted and 3.5" HD is around 750 - but 
it's been a while :-)

5.25" SD/DD was 300 IIRC, and 5.25" HD 600 - so I'd be surprised if they'd 
even format at the wrong density.

Re. head widths, I think Anders was spot-on: it's writing (including 
formatting) a 5.25" 40-cylinder disk in an 80-track drive that can cause 
problems in other drives.

I believe 40-cylinder 3.5" drives did exist, but are extremely rare.

5.25" world further muddied by 77-track drives, 35-track drives, non-Shugart 
drives (Apple etc.), drives that expect disks with hub rings and drives that 
don't (most don't care, thankfully), drives that run at funny speeds, drives 
that are fixed to a specific address etc. :-)

cheers

Jules