Unruh wrote:


> The claim is that in the past, hard drives would tend to keep traces of the
> data. But now, because the manufacturer's are trying to squeeze the last
> ounce of data out of drives, any such residual memory would be a source of
> extra storage,


This is a bogus argument. Knowing that you could increase the data density
doesn't make it any more feasible if its computationally and technically
expensive.

> so that modern disks have essentially zero redundancy and
> those old techniques do not work. Ie, overwriting once is enough.


Well, at least the corollary holds.

With increased read speeds, the signals got so badly deluded that they're
essentially pure sinus waves. Matching with triggers became impossible, so
currently its done by comparing the signal against a large list (256 or
more) of signals in parallel and integrating over the absolute difference,
just to get the best match.
Since such a technique doesn't allow for any specialized signal codes, they
were free to resort to the very expensive, generic Turbo(-like) codes. And
since they had to use these anyway, they could also use their generism and
efficiency to increase data density to close to the Shannon limit.


> Note if the data is really that sensitive, overwrite and then destroy the
> disk by a really hot fire


Nonsense. The burnt material could shield small pieces of the disc from the
heat for a very long time.

Either you have a really really long fire (hours till days) of constant high
heat, or you may simply resort to degaussing or acid.

> The current claim is that it is not actually doable on modern disks.


It is, just the results are not significantly better than educated guessing.