Older magnetic storage exhibited some data remanence, so a recommendation emerged to wipe data by overwriting it multiple times with varying patterns — the “Gutmann wipe”. More recent hard disk ...
Why is writing zeros (or random data) over a hard drive multiple times better than just doing it once?
Lots of different programs, such as Darik's Boot and Nuke, let you write over a hard drive multiple times under the guise of it being more secure than just doing it once. Why?
As storage technologies change over time, using different encodings and remappings to deal with sector errors, the best way to permanently erase/wipe/shred data changes also. Methods for flash drives ...