Re: CBM 8280

From: Andrew Vardy (
Date: 1999-09-11 22:19:14

Date sent:      	Sat, 4 Sep 1999 19:31:55 -0400 (EDT)
From:           	William Levak <>
Subject:        	Re: CBM 8280
Send reply to:

> On Sat, 4 Sep 1999, Radioactive Warrior wrote:
> > How strong a feild do those home bulk-erasers generate?  I don't own one
> > but I have seen my friend use his to blank audio tape.  How long does it
> > take for the field orient all the media particles (10 sec? 100 sec?)
> > Does it help at all to rotate the disk around the field many times to
> > 'exercise' the particles or dosen't it matter?
> Bulk erasers come in many sizes and configurations.  Whether you must
> rotate the disk depends on the geometry of the magnetic field.  Ones that

I've only seen one.  At Radio Shack.  Quite expensive where I live.

There are others?

> use electomagnets are more efficient than ones using permanent magnets.
> The electromagnet changes the magnetic field 120 (or 100) times per
> second.  It is this changing field that counteracts the residual field. I
> use an eraser designed for video tapes.  This is powerful enough to easily
> penetrate floppy disks and audio tapes with little effort. The usual
> procedure is to move the disk or the bulk eraser in a circular motion and
> gradually pull the eraser away from the disk.  Doing this 2 or 3 times is
> generally enough to restore a disk to "new" condition. Military security
> specifications prescribe the field strength and the number of times to
> bulk erase in order to get a complete erase for each type of media.  If
> these specifications are followed, residual data cannot be recovered even
> with the most sophisticated equipment.  After all, that is the point of
> the specifications.

Say, sounds interesting.  I wonder how they gather this residual 
data.  Does that mean they'd have to have programs that can read 
half tracks and half sectors?

If so, tell me more.
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