I was thinking and studing about the disk wiping topic and find out some things...
Disk pattern is a ferromagnetic plate. "Empty spaces" are positions on this plate, where a disk heads are writing the bits. The bits are writing by very simple process - there is a little electro-magnet on the disk head, which is activated by electric drive (I= ~10 to 1000 uA) and on a position, where the bit have to be writen appears a "permanent" magnetic mark, which means "1" (if there is no mark on the position, that means "0"). We now a electromagnetic problematics called "hysteresy loop", which is telling us: If we try to unmark the marked position on a disk pattern (which was magnetticaly marked before), there will be a small magnetic mark left on the "empty place", which will be polarised by other way (90 degrees forward) and will have a 6 to 10 times smaller level as the old mark. This mark is small, but, of course, can be find on a pattern. There is no way to unmagnetise the ferromagnetic material once magnetised. If somebody (probably no one :>>>>>) want to know more about hysteresy loop, please e-mail me privatelly, because it is Off Topic. You probably learned about hysteresy loop, if you did study on electrical high school (in Slovakia - 2nd and 3rd year on Railway School of Slovak Republic). That all means: If you write a magnetic mark on a disk pattern once, it stays there for allways, just will be smaller and polarised by other way (90, 180 or 270 degrees). So you probably can know allways, which positions was ever used for a bit providing an information about "logical one". That probably means that it is the way to find out what was the vallue of a bit on a disk before it was overwriten with another vallue, but it is necessary to use very, very, very sensitive equipment. I am trying to find out something about, how is the magnetic mark on a disk pattern changing in according to time and if it is possible to determine, WHAT mark was on a position in WHAT time. IMHO it is possible to recover data from a wiped disk only if that is possible. Thank You PS: Sorry, I was just wondering, how simple it is, so I wanted all of you to know it too :> Tomas Tudja 136 Church Road N17 8AJ London, UK [EMAIL PROTECTED] http://hysteria.sk/catcher
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