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There are two basic types of MiniDiscs. The Recordable MD (Diagram
1) and the Premastered MD (Diagram 2). In the diagrams at left, we
can see what the surfaces of the two types of MD look like at a
microscopic level. The Premastered MD is similar to a CD, while the
Recordable MD utilizes exciting new technology that we shall explore
further.
You are probably familiar with digitally stored music from the Compact
Disc (CD). But did you know how this music is played back, once the CD
has been inserted into a player? First, you know that "digital" means
that the data is being stored in binary code - "1's" and "0's." But how
does the CD store your favorite music, or other data, in this format?
Well, look again at Diagram 2, the Premastered MD. You'll
notice that pits have been chiseled into the surface. When the laser beam
in your CD player strikes the surface of the CD, it is reflected back. If
it strikes a pit, the reflection will be a low intensity return;
otherwise the reflection will be a high intensity return. There
you have it - the two types of reflection are assigned values of either
"1" or "0", and you have your digitaly stored music.
But you'll notice the diagram of the Recordable MD shows no evidence
of pits - so how does it store digital music? Well, let's go to the next section and find out.
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