Silly question about secure deletion of files

[David Shaw]

On Fri, Jan 23, 2009 at 05:33:12PM -0300, 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.
> 
> 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?

The two things have nothing to do with each other.  It's like asking
why human beings can't fly, but we still can eat lunch.

David