My personal knowledge is a bit stale but last I knew a step in fabrication of a hard drive was a run through a precision spinning table that wrote basic magnetic information on a disk that was intended for use by software that could "format" the platters into sectors and cylinders. It's likely that the magnetic fields used for that purpose were considerably higher than those used for normal reading and writing but it would be quite possible to destroy the information needed for reformatting were a large magnet to be used.
Permanent magnets can be used to demagnetize floppy disks. Those depend on careful alignment of the write heads on the drives for formatting of the disk and the read and write fields are high enough to saturate the hysteresis curve of the magnetic oxide. More or less high density hard drives behave like analog devices these days with the digital data being treated much like a telephone modem talking to a tape recorder only at vastly higher baud rates. A moment for an old story please: In the early 1970's my laboratory with the US Navy became aware of a bunch of small computers that were to be decommissioned by the Air Force. The thought was that each of us could actually have one on his desktop. But. . . The computers were coming out of intercontinental missiles that were being replaced in their silos with newer beasts. The disks in them contained highly classified targeting information and nobody knew how to erase them. Overwriting a few hundred times was not good enough because special techniques were available to look only at the very edges of the tracks and recover information. The computers, with their disks, were crushed. -- --> From the U S of A, the only socialist country that refuses to admit it. <-- --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed Low End Mac's G3-5 List, a group for those using G3, G4, and G5 desktop Macs - with a particular focus on Power Macs. The list FAQ is at http://lowendmac.com/lists/g-list.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/g3-5-list?hl=en Low End Mac RSS feed at feed://lowendmac.com/feed.xml -~----------~----~----~----~------~----~------~--~---
