As shown in Figure 4, the CD is subdivided into
three parts: the Lead In Track, the Program
Area, and the Lead Out Area. These three sec-
tions together are considered the Information
Area. There is a hole in the center for holding
the disc. The disc is held between two equally
sized concentric rings. The rings have an inner
diameter of 29mm and an outer diameter of
31mm.
The Data on the disc is recorded on a spiral
shaped track with pits and lands. The reflective
side of the disc contains the tracks.
The production of a disc is a high tech process
explained in Figure 5. The process starts with
glass that is photo etched. The glass is silver
plated and is used as a form for a metal cast.
The metal cast is used to stamp a nickel Mother
Stencil. The Mother Stencil is used to stamp the
Son Stencil. Son Stencils are used to stamp the
foil of the discs. A protective layer and label are
added.
Read Process
The Servo circuit is responsible for focusing the
laser and moving the Light Pen to follow the spi-
raling tracks on the rotating disc. The digital High
Figure 4 - The Disc
Figure 5 - Creating a CD
3
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