RE: [AV Media Matters] Digitizing Audio and Video-ReallyBigPost

[Peter Brothers <lists@specsbros.com>]

This effect was discussed at a recent AES/ISO joint commission meeting
in
Washington that both Jim Wheeler and I attended.  I have not seen the
research data on the effect but another attendee from NIST said he would
forward me the references.

If I recall correctly, the effect is called the "super paramagnetic
effect."
>From the discussion, it appears that with high density hard drives, the
recording pigments are so small and so close together that, over time,
the
magnetic fields of the pigments can interact, effectively "scrambling"
or
"erasing" the data.  As such, it is not an effect one necessarily needs
to
worry about with all discs, just some high density discs.

It was also mentioned that a buffering agent has been developed to
reduce
the effect but not to entirely eliminate it.

This effect is not something I can confirm since I haven't yet seen the
research, but a number of fairly knowledgeable and technically competent
experts at the meeting seemed quite familiar with it.  In any case,
there is
no physical reason why spinning the disc would have any positive effect
unless you were rewriting the data to the disc at the same time.

Peter Brothers





> -----Original Message-----
> From: alyssa@musicnorth.com [mailto:alyssa@musicnorth.com]
> Sent: Tuesday, June 03, 2003 8:04 AM
> To: AV Media Matters
> Subject: Re: [AV Media Matters] Digitizing Audio and
Video-ReallyBigPost
>
>
> Hi Jim et al,
>
> What this IT guy was getting at, was that if you shelve a HD, the disc
> will eventually lose its' magnetism, unless you spin it up from time
to
> time. I have heard this once before, perhaps it is just FUD, as
Richard
> mentioned, but I would like to know if there Is any truth to it?
>
> Best,
>
> Alyssa.
>
> Moderators Comment:
> No, there is no truth to that other then perhaps considering earths'
> magnetic field over centuries - or a more likely culprit are those
> really strong  magnets placed on some bookends used on library
> shelving..... - but there are other more important reasons not to
> consider shelving a HD and trying to recover the data years later as I
> detailed in my moderators comment to Jim Wheeler the other day.
>
> I would suggest to all interested to learn a bit about coercively and
> magnetic recording. It is covered in any decent book on recording
> technology or magentics. It is a fundamental concept in this area.
What
> is coercivity you ask??
> coercivity
>
> SYLLABICATION: co.er.civ.i.ty
> NOUN: The intensity of the magnetic field needed to reduce the
> magnetization of a ferromagnetic material to zero after it has reached
> saturation
>
> Hard Drives have high coercivity - so it will take a strong magnetic
> field in close proximity for a period of time to really cause a
problem.
>

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