Data Erasing Question

I have a question for somebody more knowledgeable than myself: Why do erasing applications have to use "complicated patterns" of bits to overwrite data that is on a disc, over and over again. Setting every bit to 0 would eliminate any traces of anything, wouldn't that be much simpler?

I am no expert in the field but simply 'resetting' as you put it to zero is claimed to be reversible(not really sure on how honesty). Thus, we turn to deleting styles such as gutmann delete which will delete a file 35 times. It is important to note however that hard drives have changed considerably since gutmann was conceived which renders several of the patterns that it uses obsolete.

While I don't know of any particular technology that can actually reverse an overwrite, if you have data you really wish to hide its probably better to be safe side and go with the overkill.

http://en.wikipedia.org/wiki/Hard_disk_drive that has some info on how data is stored on a HDD.

Short Version Data stores itself magnetically on the HDD platters. Overwriting something is not really perfectly clean. Imagine writing something on paper, erasing it, and writing on it again. There are still ways to see the original. (I know its not really the same, but gives you the picture) Doing this multiple times blurs it more and more.

Though if you really want a clean hard drive as if it were never used, you can degauss it (place it next to a huge magnet) and all the data will be completely wiped clean.

I like that version. Much simpler. I just wanted to add that to get a better understanding of why apps overwrite instead of just zeroing, look up electromagnetic microscopy.