light reflecting from the disc. The pulses are
created by Pits in the Reflective Layer of the
disc. The Pits reflect less light than the intact
surface of the Reflective Layer, called Lands.
Disc Mechanical Layout
The DVD and CD share much of their tech-
nology. We will start with CDs and work our
way to the DVD. The CD is a plastic disc
120mm in diameter, with a thickness of
1.2mm. Refer to Figure 3. It has a silver col-
ored Reflective Layer. The maximum playing
time for a music recording on a Compact
Disc, CD, is 74 Min.
The CD is less vulnerable to damage than an
analog record. That does not mean it does
not have to be treated with care. Dirt and
heavy scratches can interfere with playability.
Figure 2 – CD Laser Operation
Figure 3 – Mechanical Layout of a CD.
2
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