Magnetic Media for Long Term Archival
By Larry Fisher
>
> From: "Thomas Henden" <Thomas.Henden@stud.hf.hioslo.no>
>
> Subject: DISKS AS A CONSERVATION MEDIUM
>
> One should remember that even if the magnetic material on those media
> could be made to last forever, the magnetic orientation of the atoms
> in it will not
> The only safe way to store magnetic media would therefore be in a
> 'Farady' s cage' which really is what the name says, a cage, if you
> like it, a bird cage, that is connected to earth. (grounded)
>
> That means indeed, it is a bit impractical to make a 100% magnetic
> field-less storage for any magnetic recording, be they disks or
> tapes.
>
> [ I don't think a field-less storage vault is required for magnetic
> [ disks and tape. One of the desirable properties of digital magnetic
> [ media is that it has a very peculiar B-H curve. Specifically
> [ it takes a very strong applied magnetic field to get the
> [ stored magnetic state to change. Once changed, it takes an
> [ equally strong opposite applied magnetic field to get the
> [ stored magnet state to change back. In particular, the strength
> [ of applied field required is much larger than any ambient (earth,
> [ etc) magnetic field. Otherwise, these digital medias would be essentially
> [ useless. I don't think that the stored magnetic field degrades with
> [ time, unless the atoms can physically migrate in the medium (i.e. how
> [ rigid is the [ coating on or in the plastic)
> [
I've put a 3 1/2" floppy flat against a rather large speaker magnet for a minute or two trying to destroy the format. The disk suffered no noticeable loss of data. I realize I only exposed it to a possible exponentially larger magnetic field than that of the earth, for only a fraction of time compared to many years of storage, but the idea that the data held up to that level of magnetic abuse was impressive. Storage media must be upgraded from time to time. To be able to read the old media and process it for storage on the new media is the key. I'm happy to see so many people concerned about preserving the old paper rolls for transferring to a newer media. It would be a shame to loose all the work and authenticity that went into some of the rolls that are now becoming very brittle.
Lar
Larry Fisher RPT, Metro Portland, Oregon's
Factory Preferred Installer for MSR/PianoDisc Products
phone 360-256-2999 or email larryf@pacifier.com
http://pacifier.com/~larryf/homepage.html
the piano's keyboard smiled at me & said, "I dare ya to tune me!" |
(Message sent Tue 12 Mar 1996, 00:51:29 GMT, from time zone GMT-0800.) |
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