Before we find out exactly how the Recordable MD stores music, or other
information, digitally, let's examine what the disc looks like up close
first. Diagram 3 at left shows a cross-section of a Recordable MD. Here
are the different layers:
- The Protective Layer
- The Reflective Layer
- The Dielectric Layers
- The Magnetic Layer
- The Disc Substrate
Important Layers:
While all the layers above are essential to the Recordable MD, the layers
that actually differentiate it from the Premastered MD are the
Magnetic Layer (D) and the Dielectric Layers (C). These
layers serve the important role of recording as well as playback.
The Other Layers:
The Protective Layer, as its name suggests, protects the recording
layer from the outside environment. Furthermore, a lubricating agent has
been added to this layer to optimize conditions for the magnetic
recording head above the disc. The Reflective Layer performs
optical science's reflective and heat absorbing functions. The Disc
Substrate, made of the same polycarbonate resin found in CD's,
provides superior reliability and durability.
Now you know what a vertical cross-section of an MD looks like, and the
various functions its different layers perform. But the question remains:
How does the Recordable MD actually record? Let's find out in the next section.
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