The data is contained in the order of the
chain of changed/unchanged areas. Articles I have read suggest a lifetime of
30-50 years or more for a CDR stored in a normal indoor environment. For as
long as the CD is readable, though, the entire lot of the data will be
readable (as I choose to define 'readable' i.e. recover the original data in
full) thus enabling the reconstruction of the original image without loss of
its integrity as it was stored originally.
This is not as black and white(sorry) as it seems. People are losing
data irretrievably on recordable CDs in a few months in some cases.
The only thing that can be said for this is that while a digital
archive image is actively maintained there can be 1000f the original image
data updated and transferred to the new medias and formats.
That is 1000f the scanned information which is not the same as the
original - the difference between an original Ansel Adams print and
calendar page litho.
While this discussion has academic interest for most of us, I wonder how
NASA is preserving the original images of the moon landings, etc...? I would
suggest highest quality digital scans, and then also archive the color
information from the color negatives/slides to black & white RGB-filtered
images, thereby changing the color dye information into monochrome silver in
emulsion information. This probably is longer lasting than color chemistry,
as Matthew Brady's Civil War negatives suggest.
That seems to be a changing opinion too. Apparently modern black and
white materials are not as long lived as Brady's emulsion on glass
plates. The whole longevity thing is really up in the air and
everyone's well thought out solutions seem to be just educated
guesses. Maybe if the image was etched into a stone tablet and buried
in a tomb in the desert?
Cultural and historical considerations aside I guess there is no need
to go into the philosophical/psychological questions of the urge to
preserve the mementos of our lives.
--
Winsor Crosby
Long Beach, California
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