Hi,
I would like to add some info that I googled to this interesting topic:
There are 2 kinds of formatting methods avail:
1.
High level format (also known as quick format)
Only rewrites the File Index(Master boot record, File Allocation Table, Master File Table) of the media and makes the whole space available for writing data. Althought physically, previous data is still present, only marked as free space.
Data is almost fully recoverable.
2.
Disk Reinitialization (also known as Low level format / Default Format)
Every sector of the drive is written to by writing a zero byte to every addressable location on the disk.
Recovering overwritten data
When data has been physically overwritten on a hard disk it is generally assumed that the previous data is no longer possible to recover. In 1996, Peter Gutmann, a respected computer scientist, presented a paper that suggested overwritten data could be recovered through the use of Scanning transmission electron microscopy.[3] In 2001, he presented another paper on a similar topic.[4] Substantial criticism has followed, primarily dealing with the lack of any concrete examples of significant amounts of overwritten data being recovered.[5][6] To guard against this type of data recovery, he and Colin Plumb designed the Gutmann method, which is used by several disk scrubbing software packages.
Although Gutmann's theory may not be wrong, there's no practical evidence that overwritten data can be recovered. Moreover, there are good reasons to think that it cannot.[7][8]
Feasibility of recovering overwritten data
Peter Gutmann investigated data recovery from nominally overwritten media in the mid-1990s. He suggested magnetic force microscopy may be able to recover such data, and developed specific patterns, for specific drive technologies, designed to counter such.[1] These patterns have come to be known as the Gutmann method.
Daniel Feenberg, an economist at the private National Bureau of Economic Research, claims that the chances of overwritten data being recovered from a modern hard drive amount to "urban legend".[2]
"Surveying all the references, I conclude that Gutmann's claim belongs in the category of urban legend.
Or it may be in the category of marketing hype. I note that it is being used to sell a software package called "The Annililator". "
As of Nov 2007, the DoD considers overwriting acceptable for clearing magnetic media, but not as a sanitization method. Only degaussing or physical destruction is acceptable for the latter.[3]
On the other hand, according to the 2006 NIST Special Publication 800-88 (p. 7): "Studies have shown that most of today’s media can be effectively cleared by one overwrite" and "for ATA disk drives manufactured after 2001 (over 15 GB) the terms clearing and purging have converged."[4]
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References:
<a href="https://en.wikipedia.org/wiki/Disk_formatting" target="_blank" rel="nofollow noopener noreferrer">Disk formatting - Wikipedia</a>
<a href="https://en.wikipedia.org/wiki/Data_recovery" target="_blank" rel="nofollow noopener noreferrer">Data recovery - Wikipedia</a>
<a href="https://en.wikipedia.org/wiki/Data_recovery" target="_blank" rel="nofollow noopener noreferrer">Data recovery - Wikipedia</a>
Personally, I think it's not totally impossible to recover data "bit" by 'bit", as data is a sequence of "1 and 0 bits" (8 bit being 1 byte).
But it would be extremely COSTLY, requiring a high level of forensic expertise in a "clean room" and plenty of patience. Thus, nearly an impossible task to undertake.
