There are different ways of making CD disks, and the manufacturers make
various claims, but so far no one has said that a disk can last as long as,
say, a clay tablet pressed with cuneiform script or a papyrus sheet written
by an Egyptian scribe. Those pieces of writing have lasted a few thousand
years.
In addition to having the disk deteriorate, there's the problem of having
the reading technology go obsolete. People who wrote to old fashioned floppy
disks (the real floppy kind) have had to transfer their documents to
currently manufactured CDs, because nowadays most computers can't accept
those big disks. Whenever there's an upgrading of media technology a lot of
material gets left behind, abandoned and forgotten, lost.
The music industry shows this most dramatically. Record players manufactured
in the late 1960s and 1970s were designed to play records at 78, 45 and 33
revolutions per second. That was technologies attempt to preserve the
availability of recordings made over the previous fifty years. But with the
advent of digital recording and playback, those old 78-, 35- and 33-rpm
disks had to be transferred to digital media to be heard, and most disks
were simply left behind.
All of which brings us back to the letters of John and Abigail Adams. The
primitive technology of the Eighteenth Century worked back then and it still
works today. We can read those old letters, and if we want to we can write
with ink on paper. But very likely in fifty years nobody will be able to
read our email or any other document written by laser light on a CD.
—Gene M.