Actually, it doesn't require a microscope. All current hard drives adjust the track location to compensate for expansion of the platter because the temperature has changed and other little details. What is required is a diagnostic controller that can adjust the head position just to the side of the track so it can read prior data. Some of what can be read in relatively short time is close to magical. The multiple pass requirement is so the head position is at different parts of the track tolerance which will reduce the ability of a diagnostic controller to easily read the data. Note - this does not make it impossible just harder. and yes the electron microscope is still the final recovery tool.
That is the reason for the requirement for physical destruction for some kinds of data. Mike On 6/29/05, R.S. <[EMAIL PROTECTED]> wrote: > SArnett wrote: > > > Just out of curiosity, why multiple passes. I know that they must have > > their reasons... Something like residual data on the edges of the track > > or some such, since there is a possibility of the track not being > > recorded in the exact location of the previous write? > > It is (theoretically) possible to read "traces" or "remains" from disk > plate. It is analog device, magnetism is not 0 or 1, sometimes it can be > 0.05 (it suggest 1 before the erasure), or 0 at the middle of the track, > but 1 on the edges. > Lats but not least, it is virtually impossible to read overwritten data > using regular controller (microscopes are used), it is rather "most > probable" track content rather then just track content, it is veeeery > hard work to assemble the bits into any informative string of data. > However it is possible. > IMHO more possible would be to corrupt any employee having access to > data. And much less expensive. > From the other hand "special" agencies like NSA (where it would be much > harder to corrupt employee or employee cannot steal the data) for sure > uses their owne erasure methods or just destroy the disks. > > -- > Radoslaw Skorupka > Lodz, Poland > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO > Search the archives at http://bama.ua.edu/archives/ibm-main.html > -- Mike ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
