The following is a Plus Edition article written by and copyright by Dick Eastman.
CD discs (often called “optical discs) have been commercially available since the 1980s. Sadly, many computer users have inserted their older CDs into a computer and found that the discs no longer work.
Sometimes it is a software problem: the old software for the CD might not work on a newer version of Windows or Macintosh. However, the most common problem seems to be physical: the CDs themselves have microscopic mold or "rot" that ruins the surface and prevents the data from being read. Even worse, there is no cure. If the data is bad now, it will only get worse. There is no reliable way to restore data from a defective CD.
Some experts claim that CDs will last up to 200 years. However, practical experience shows that hasn't happened in the first 30 or 40 years. To be sure, not all CDs have gone bad. Only a percentage of them have failed so far. Perhaps the MAJORITY will last 200 years or the AVERAGE will be 200 years, but we know it will not be true of 100% of the discs. However, nobody knows how to predict which disc will fail next. The CD that is most valuable to you might last another 170 years, or it may fail tomorrow.
We do know that CDs created one at a time in a PC do not last as long as CDs created in a factory, where hundreds of them are made at once. Those backups you made or that family genealogy book you wrote may not last very long on a CD you "burned" at home.
To understand what limits the life span of optical discs, let’s look at how they are built. What all optical discs have in common is the presence of three key layers:
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