When i worked a contract for the military years ago they had to cycle 1,s and 0's to mag tapes nine times before unclassifying the media. These tapes had bigger "dots" than modern media, so maybe harder to erase, but we have better detectors now too. I would think that if you dd 0's then 1's 9 times you would more then exceed the technological capabilities of a curious lap top manufacturer employee. I don't know the commands to do that. Charly Baker On Monday December 6 2004 11:11 am, James Knott wrote:
Jeffrey L. Taylor wrote:
This isn't sufficient for a sufficiently determined and resourceful adversary. E.g. the intelligence services of major countries and corporations.
Magnetic disks are analog, not digital. E.g., setting a bit to 1 then 0 results in a slightly different magnetization levels and spatial patterns than setting it to 0 twice.
However, each time you overwrite, the orginal data gets pushed further down into the noise, making it more difficult to read. Eventually, a point will be reached, when it's impossible to tell the original data, from the noise. There is IIRC, a specified number of overwrites, with different patterns, so that the disk is considered fully erased.