From: James Rogers (jamesr@best.com)
Date: Sat Apr 17 1999 - 15:12:03 MDT
At 01:25 PM 4/17/99 -0400, you wrote:
>James Rogers wrote:
>
>> The biggest problem is deterioration of the media. The storage life of CD
>> media isn't even close to 50,000 years. Normal aluminum film CDs are only
>> good for about 100 years and recordable CD media is around 20 (although it
>> varies widely depending on the type). The longest lasting ones, gold film
>> CD masters, will last less than 1,000 years.
>
>What are the criteria for decay of the media?
Decay of CD media is usually due to chemical reactions between the
different layers of the media or with the environment. Ionizing radiation
is a primary culprit, both directly and indirectly.
The recordable CDs have organic/metallo-organic recording surfaces that are
by their nature more susceptible to ionizing radiation, heat, and oxidation
than the metal media. However, the rapidity of decay varies widely
depending on which of the many types of recording surfaces is used, ranging
from 10 to 75 years of useful life with most being around 20-25 years.
Normal production CDs have an aluminum recording surface. The aluminum
slowly oxidizes, either by exposure to atmospheric oxygen (it leaks in
along the exposed edges), or from very slow oxidation reactions with the
surrounding media.
Gold film masters have a gold film recording surface that is essentially
impervious to oxidation. Unfortunately, the polymer media layers
surrounding it (polycarbonates et al) will degrade to the point of ruining
the media over a few hundred years, mostly as a function of exposure to
ionizing radiation.
It would be possible to design a read-only media that could last 100,000
years without degradation, but there is not enough of a market to justify
the cost over current solutions. Most people are satisfied with media that
will probably outlive them.
My knowledge of this comes from when I worked in the recording industry.
This was and is a big deal, since a huge amount of money is invested in the
information stored on mastering media, and a good master can maintain a
commercial value of some type for a century or more.
-James Rogers
jamesr@best.com
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