Re: Magnetic fields and Storage Devices

[Bernard Cleyet <anngeorg@PACBELL.NET>]

You'll find much information (detailed) by searching using, e.g.
coercivity "magnetic media"; for other media drop the quotes.

Practically, I have a bulk eraser that erases well type I (rough), but
requires repeated use for more modern formulations.  It induces in a one
turn loop 3 cm. diameter ~ 50 mV.  The separation is the insulation of
the wire.  Increasing the separation ~ 7 mm reduces the induced PD to ~
30 mV.  ("You do the math.")  This distance more closely approximates
the nearest distance to tape in cassettes.  I expect HDs * to have the
sam formulation as the best archival tape or similar to digital
recording tape.  Since magnetic media have a relative permeability some
what grater than one, the externally applied field will be somewhat
greater than found from the above calc.

* A BTW: early sixties technology for HDs was to spin the drum and spray
the iron oxide(s) with a paint sprayer.  I'm referring to the quasi-RAM
in a desk computer (not desk top!).  It had 64 read write heads, and
when worth the time, the programs were written so the head was just
waiting for the addressed blocks when it arrived instead of waiting for
almost a full revolution.

bc

J. Green wrote:

> I was wondering the other day how big of a magnetic field would be needed to
> "erase" a magnetic storage device (floppy, removable tape, hard drive,
> etc...).  Does anyone have any experience or idea?
>
> Josh Green