Re: How to damage a floppy?

[mjmahon@aol.com (Michael J. Mahon)]

>Yah. A constant magnetic field does almost nothing. It is the speed at which
>it's changing that determines how much effect it has on the coating.

Actually, if you're only interested in changing the magnetic
state of the oxide's domains, the _only_ thing that matters is the
_magnitude_ of the field, not it's rate of change.  When the field
magnitude exceeds the critical value for the medium, determined
by its hysteresis (which allows it to "remember" a magnetic
state), then it will change state and the info stored in that location
will be altered.

AC fields of decreasing amplitude are great for demagnetizing things
(i.e.:  leaving them with near-zero magnetization), but just
changing the magnetization is enough to scramble the bits.

-michael

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