Originally posted here by spyrul


actually, i'm pretty sure that it's completely infeasible to get overwritten data. think of it this way:

you have a closet full of empty Coke cans. you've documented how many Coke cans you have in there.

so, for now, a Coke can is data, and your little documentation would be your file allocation table.

now, you want to get rid of some Coke cans. initially, you just erase a few numbers off the documentation, and, as far as you're concerned, you've got more room in your closet. let's say you erase the entire documentation, and now you want to fill the closet with beer cans. because there's not enough physical room to store more than a couple of beer cans, you toss a bunch of Coke cans in to the hall, then place the beer cans in there and document that.

now there is no way to look in the closet and find Coke cans. before you say "you can retrieve them by going in the hall and picking them up", keep in mind that the HDD doesn't have a hallway it can toss its empty Coke cans in to
Well, no, IT IS possible:

Overwriting data on disk isn't like filling a closet, it's like writing over used paper... What happens is that when the disk heads write on the platter, it re-aligns magnetite (or whatever magnetic compound they use) in a diffrent direction. However, a single write doesn't manage to get all magnetite (or whatever) particuls re-alligned. So while the majority of particuls will have change directions, there will be a few residual ones that will still be oriented in the previous direction.

So finding out what data was there before means using a more sensible device that can distinguish or detect variations in the magnetic field or such... (That's why whiping software will make multiple writing passes, sometimes with randomized caracter, in order to try and re-allign all particuls). Of course this is hard to do and pretty expensive, but people with enough money and resources (think FBI, CIA, NSA...) could and do have the means to do it. In fact, I remember reading somewhere that it was rumored the NSA (I think) was able to recover data after 27 passes!

Ammo