CD is short for Compact Disc.
A compact disc is constructed of 5 separate layers…
1. A thick, soft, clear plastic layer.
This layer comprises the majority of the CD's thickness
and weight. It protects the data layer from damage on
the play side and it acts as a lens to focus the CD
player's laser onto the data layer so it can more easily
read the data.
2. The data layer is where the music
and any other information are stored. It's the layer
that the CD player "reads" in order to create
the music, graphics, etc. The data layer is moulded
or pressed into the top of the clear plastic layer.
The data in the data layer is arranged in tracks that
spiral like the grooves on a vinyl record, except CDs
are read from the "inside out", the opposite
of vinyl records.
3. Next, a reflective, metallic layer
is placed on top of the data layer. It allows the disc
to function like a mirror, reflecting the CD player's
laser back to the detector in the CD player after it
has read the data layer. This layer gives the CD's play-side
that shiny appearance.
4. A thin, hard protective layer is
an ultra-thin plastic coating added to provide protection
of the reflective and data layers, while also forming
a surface upon which the label information can be printed.
5. Finally the label layer is printed
on top of the protective layer. It contains. for example,
the CD title, graphics, band name and other information
to identify the contents of the disc. That's the label
side, of course.