On Jan 27, 2009, at 10:53 PM, Kris Tilford wrote:
> > On Jan 27, 2009, at 9:25 PM, Bill Connelly wrote: > >> Why isn't "1 Pass", Writing Zeroes, sufficient to wipe a disk clean? > > There exists special hardware/software that can scan a disk for the > strength of the magnetism of each individual bit. There is a residual > magnetism each time a bit is erased. As an example, if the residual > was 10% (a convenient size for this example), and the initial bits > were 0 and 1 (relative values), then the first write would be 1, and > the first erase would be 0.1 (10% residual charge). The second write > would be 1.1 and the second erase would be 0.11. After a series of > reads & writes, the actual value of the magnetism of each bit retains > a "record" of its past values within the "exact" magnetism. In this > artificially convenient example, the values will only be 1's or 0's, > so if you measured the value of a bit as 1.0110111 this would tell you > that the current value is 1, the the previous seven values were > 0,1,1,0,1,1,1 respectively. It's not this simple in real life, but > "theoretically" you can reconstruct erased and rewritten data. > >> Isn't that "7 Passes", a DoD (Department of Defense-iveness) >> government hoopla/hangup/thingy? > > I've read somewhere the CIA or someone had the precision to get the > previous 13 read/write cycles. I'd guess this is "really difficult", > but what do I know, perhaps it's been automated? > OIC. Maybe an "MRI" would do it. Bill Connelly artsite: http://mysite.verizon.net/moonstoneartstudio myspace: http://www.myspace.com/moonstoneartstudio --~--~---------~--~----~------------~-------~--~----~ 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 g3-5-list@googlegroups.com To unsubscribe from this group, send email to g3-5-list-unsubscr...@googlegroups.com 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 -~----------~----~----~----~------~----~------~--~---
