Silly question about secure deletion of files

[Robert J. Hansen]

Faramir wrote:
> Well, I already know why it is not reliable to "securely delete" a file,
> I understand the hdd can do the "overwrite" process in the "wrong" place
> of the hdd.

Right.

> But yesterday I had to defrag my hdd, and that made me wonder: why we
> can't overwrite a file, but we still can defrag the hdd? Is there a
> hardware feature that allows SO to defrag the hdd?

Not really.  It's more a question of context.

With a defrag, if you successfully rearrange 95% of the affected blocks
then you've substantially improved your drive performance.  Sure, it'll
report that it's done 100%, but who cares, really?

With disk overwriting, if you successfully overwrite 95% of your
sensitive data, you may still be putting yourself at substantial risk.
Especially since it will report that it overwrote all your data.