Re: Good source for "new" 5.25 and 3.5 inch floppy disks?

["Michael J. Mahon" <mjmahon@aol.com>]

glen herrmannsfeldt wrote:
> Michael J. Mahon wrote:
>
> (snip)
>
> > If you're not sure, and you care about the permanence of your data,
> > HD media in DD 3.5" drives should be avoided.
>
>
> As far as I understand it, it either will or won't write.
> There is a very small probability of a partial write,
> somewhat similar to a coin flip landing on the side.

The coercivity specifies the field strength necessary to switch the
media from one saturated state to another.

If the media was previously recorded, then you are correct--the media,
or at least substantial parts of it, are already saturated in one or
the other direction, and write current will either be sufficient to
change it or not.

However, if the media is not recorded, or has been degaussed, then
smaller write currents will be sufficient to cause a partial response
and leave the media in a lower state of magnetization.  In this case,
the disk could read correctly for a while, but would have a lower
read signal and a lower threshold for data disturbance.

> > As noted before, a DD 5.25" drive will *not* reliably write HD media.
>
>
> With a factor of two in coercivity for 5.25in it is pretty much
> zero chance.  Note that core memory depends on half the current not
> writing a bit for every write or read cycle.

Excellent point!

-michael

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