Hardware Reference
In-Depth Information
After the specification was set, both manufacturers were in a race to introduce the first
commercially available CD audio drive. Because of its greater experience with digital
electronics,SonywonthatraceandbeatPhilipstomarketbyonemonth,whenonOctober
1,1982SonyintroducedtheCDP-101playerandtheworld'sfirstcommercialCDrecord-
ing—BillyJoel's 52nd Street album.TheplayerwasintroducedinJapanandthenEurope;
itwasn'tavailable intheUnited States until early 1983.In1984,Sonyalso introduced the
first automobile and portable CD players.
Sony and Philips continued to collaborate on CD standards throughout the decade, and in
1983 they jointly released the Yellow Book CD-ROM standard. It turned the CD from a
digital audio storage medium to one that could now store read-only data for use with a
computer. The Yellow Book used the same physical format as audio CDs but modified
the decoding electronics to allow data to be stored reliably. In fact, all subsequent CD
standards (usually referred to by their colored book binders) have referred to the original
Red Book standard for the physical parameters of the disc. With the advent of the Yellow
Book standard (CD-ROM), what originally was designed to hold a symphony could now
be used to hold practically any type of information or software.
For more information on the other CD book formats, see the section “ CD Formats , ” later
in this chapter.
CD Construction and Technology
A CD is made of a polycarbonate wafer, 120mm in diameter and 1.2mm thick, with a
15mm hole in the center. This wafer base is stamped or molded with a single physical
track in a spiral configuration starting from the inside of the disc and spiraling outward.
The track has a pitch, or spiral separation, of 1.6 microns (millionths of a meter, or thou-
sandths of a millimeter). By comparison, an LP record has a physical track pitch of about
125 microns. When viewed from the reading side (the bottom), the disc rotates counter-
clockwise. If you examined the spiral track under a microscope, you would see that along
the track are raised bumps, called pits , and flat areas between the pits, called lands . It
seems strange to call a raised bump a pit , but that is because when the discs are pressed,
the stamper works from the top side. So, from that perspective, the pits are actually de-
pressions made in the plastic.
The laser used to read the disc would pass right through the clear plastic, so the stamped
surface is coated with a reflective layer of metal (usually aluminum) to make it reflective.
Then the aluminum is coated with a thin protective layer of acrylic lacquer, and finally a
label or printing is added.
 
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