As a result, they advocate applying the voodoo to PRML and EPRML drives even though it will have no more effect than a simple scrubbing with random data. 35-Pass: it writes zeroes 35 times, and takes a very long time.Gutmann himself has responded to some of these criticisms and also criticized how his algorithm has been abused in an epilogue to his original paper, in which he states :In the time since this paper was published, some people have treated the 35-pass overwrite technique described in it more as a kind of voodoo incantation to banish evil spirits than the result of a technical analysis of drive encoding techniques.A 7-pass erasure using random data will do a pretty complete job to prevent reconstruction of the data on the drive. 7-Pass: this writes zeroes seven times over the free space, and takes seven times as long.Wipe Free Space - Multi-Pass ? Stupid Thing ? That is, for ATA disk drives manufactured after 2001 (over 15 GB) clearing by overwriting the media once is adequate to protect the media from both keyboard and laboratory attack." If there are four "north-south" fields in a row it would result in the bits "1111" being read which is the binary code for "F" hex.Yes, a weak image remains ~ if I recall correctly the mathematical chance of interpreting this weak image correctly is about 53% per bit after a single overwrite?But it doesn't really matter considering the time and cost it takes.The reason for more sophisticated methods for government data comes from stuff like bad blocks or HPAs which are not accessed by software or even failures as simple as someone unplugging a disk before the process was finished."Basically the change in track density and the related changes in the storage medium have created a situation where the acts of clearing and purging the media have converged. How can you store 1 Byte of data on a storage device that only has two states? 1 bit is the smallest storage unit and is how data is written on a magnetic hard disk.Each tiny storage unit is an oriented magnetic field ("north-south" or "south-north") which represent the bits "1" and "0".
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