The CD
or compact disc was an electronic, digital recording
medium introduced about 1997.
Electronic "photography" which
isn't photography at all as no chemistry is involved, is a digital
process of mathematically defining each picture element or
pixel.
Even a simple "photograph"
yields millions of pieces of description.
Those packets of data
may be recorded on a plastic disc which is written (or "burned")
and read by a laser.
In that way, the CD substitutes for film.
While a well protected piece of film may last 250 years or so,
the CD is much more durable and may last ten times as long (if
anyone's able to view it or cares enough to look).
Estimated basic value: $9
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