Re: Platinum 5.25" drive problem

[russotto@wanda.pond.com (Matthew Russotto)]

In article <20010711191747.17797.00005714@ng-cg1.aol.com>,
Michael J. Mahon <mjmahon@aol.com> wrote:
>Matthew Russotto wrote (in response to me):
>
>>In article <20010710181837.03517.00004552@ng-fi1.aol.com>,
>>Michael J. Mahon <mjmahon@aol.com> wrote:
>>>
>>>In short, don't worry about using permanent magnets to disrupt the
>>>magnetic patterns recorded on floppys (but don't magnetize the hub
>>>of a 3.5" diskette--that's not good.  ;-).
>>
>>You can't damage the head with a magentized floppy.  But you can make
>>the floppy unusable until demagnetized.  Bulk erasers use an AC field,
>>and attenuate it gradually at the end of the cycle.
>
>The erase and write heads of the floppy drive are, by definition, strong
>enough to deal with magnetic media in ANY state of magnetization.

Even supposing the floppy drive fully magnetizes the part directly
under the head, the parts just off-track will see a smaller field and
therefore become less magnetized.  If some external source strongly
magnetizes the off-track parts of the media, the stray fields may make
reading and writing the floppy unreliable until it is demagnetized.
Something like this happens when you try to re-write a low-density
floppy on a high-density drive (even using low-density mode).

>I would not depend on a monitor degausser to erase a floppy, but
>neither would I hold a floppy I cared about near one during the
>degauss cycle.  ;-)

I've used the trick when I had floppies which would crash the machine
(Macintosh) when inserted (due to software issues, not hardware).  A few
zaps and they could be re-initialized.  Didn't have to erase the whole
thing, just sufficiently corrupt the master directory block.
-- 
Matthew T. Russotto                                russotto@pond.com
"Extremism in defense of liberty is no vice, and moderation in pursuit
of justice is no virtue."