Longevity of CDs

Digital imaging of archives and other digital preservation often
uses CDs to store data. Are they *really* safe?  I believe Kodak
demonstrated that the polyester sandwich of a writable CD will last
for up to 100 years, and music CDs are known to play fine when badly
scratched or damaged.

My question is: Music CDs can play when damaged as the player
*interpolates* to replace missing data - in music there is a lot of
redundancy, the music in one  fraction of a second being
substantially the same as in the previous and next fraction of a
second. But with data, this is surely not the case. Can one scratch
could damage a file enough to be unreadable, turn a picture into
gibberish or whatever? Or would it only affect a tiny portion (lose
a couple of words, for example)?

Mark Clarke
London
+44 941 101 251

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                  Conservation DistList Instance 11:22
                 Distributed: Friday, September 5, 1997
                       Message Id: cdl-11-22-014
                                  ***