Kees, The potential to read overwritten data comes from the fact that the heads never "perfectly" line up in the same place twice. A write may write over 95% of the bits in a given track leaving a shadow of old data that can be read - with great difficulty and very slowly, but it can be read.
Secure erasure through multiple overwrite and patterns is meant to wipe out the shadow of old data based on the precision of heads. After enough writes over "almost" the same place the head is expected to have settled over all the surface area it has previously written to. Whether there is an industry scanning old disk drives, or labs full of spooks doing this I do not know. The thing is it can be done, and erasure is a way to prevent it or make it hard to do. The number of overwrites required to wipe the data would depend on the precision of head technology as this is what leaves residual magnetic images in the first place. Ron > > No. > > Unless I missed a part of the discussion, all statements that > overwriting once is not good enough, were based on rumours, > assumptions, > theoretical possibilities and negative evidence (data is suggested to > be > readable until proven otherwise). If my video store says a video is not > available and another store can deliver it, does this prove that all > video stores that say a video is not available are lying? Is there some > report, investigation, official statement to *prove* that overwriting > once is not good enough? > > Kees. ---------------------------------------------------------------------- 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
