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 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. - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail cbm-hackers-request@dot.tcm.hut.fi.
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