[Gllug] Thoughts on secondhand server guide price

[Peter Corlett]

On Wed, Jun 17, 2009 at 11:15:30AM +0100, Philip Hands wrote:
[...]
> So, let's say that a field strength of 1 (of whatever unit) is meant to be
> a logical 1, and 0 represents 0. The normal controller will probably treat
> anything over 0.6 as a 1, and anything under 0.4 as a zero.

That's a very simplified model of how magnetic media works, which probably
hasn't been valid for over a decade. Indeed, much of the common wisdom
regarding erasing hard disks - notably the 35-pass meme - seems to be based
on obsolete pre-IDE disk technology. Does anybody here still store critical
data on RLL-formatted Winchester drives?

Contemporary hard disks write with such a high density that individual bits
are no longer directly discernable, requiring complex DSP algorithms and
strong error-correcting codes to figure out what the data is. Overwriting
the data just once will cause the trace of the previous data to fall below
the noise floor.

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