Similarly, for some types of media, there are actual irreversible physical changes that result from writing to the media (for example, flash storage degrades a bit each time it's written to), though this may be difficult to detect without destructive testing of the media.Īdditionally, with some media types, the actual data being 'overwritten' may not in fact get overwritten for quite some time afterwards. Most modern storage devices do some form of remapping of bad sectors/blocks/bytes, and old data can still inger in those previously used and now bad areas of the media.
However, just like with correction fluid, this does not guarantee that the data can't be recovered, and even if it does prevent recovery of the exact data, it usually does not remove evidence that there was ever any data there. For traditional hard-drives zeroes are historically preferred because that results in the appearance of blank media, though some people preferentially use random data (this is preferred if you're going to re-use the media with full-disk encryption, as it will hide how much data you've got stored on the device), and for some flash drives it's better to use bytes with all the bits set (because that's how an unprogrammed cell of certain types of flash memory looks). The exact pattern technically does not matter in most cases, as any overwrite of a byte on a storage device will replace what's stored there. The simple answer is that it's (mostly, see below) the same as covering an entire printed page with correction fluid, you're just replacing the information that's there with blank space.
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