Magnetic discs: I agree with you that it ought to be possible in principle, although I find it unlikely that data recovery companies would pass up revenue when

Magnetic discs: I agree with you that it ought to be possible in principle, although I find it unlikely that data recovery companies would pass up revenue when they're quite able to do it. The only explanation to me would be that they're being paid off by somebody, e.g. governments, but again... WHY? My theory is that it used to be possible, back when the data density was much lower, larger chunks of material were involved. SSDs: I would have thought that decoupling the flash chips from the controller logic is the easiest way to get at any hidden data. You'll have to piece the data together unless you can reverse-engineer the load-balancing algorithm, although there won't be much left after one pass of zeroing anyway. I have my doubts that you can get at residual charge from previous bit values in a useful way.