Optical Storage - Upgrading and Repairing PCs - page 649

Otherformats,suchasCD-R(CD-recordable)andCD-RW(CD-rewritable),expandedthe
compact disc's capabilities by making it writable.
Older CD-ROM discs held 74 minutes of high-fidelity audio in CD audio format or
650MiB (682MB) of data. However, the current CD-ROM standard is an 80-minute disc
with a data capacity of 700MiB (737MB). When MP3, WMA, or similar compressed au-
diofilesarestoredonCD,severalhoursofaudiocanbestoredonasingledisc(depending
on the compression format and bit rate used). Music only, data only, or a combination of
music and data (Enhanced CD) can be stored on one side (only the bottom is used) of a
120mm (4.72-inch) diameter, 1.2mm (0.047-inch) thick plastic disc.
CD-ROM has the same form factor (physical shape and layout) of the familiar CD-DA
audio compact disc and can, in fact, be inserted into a normal audio player. Sometimes
it isn't playable, though, because the player reads the subcode information for the track,
which indicates that it is data and not audio. If it could be played, the result would be
noise—unless audio tracks precede the data on the CD-ROM. (See the section “ Blue
Book—CD EXTRA , ” later in this chapter.)
Accessing data from a CD using a computer is much faster than from a floppy disk but
slower than a modern hard drive.
CDs: A Brief History
In 1979, the Philips and Sony corporations joined forces to coproduce the CD-DA (Com-
pact Disc-Digital Audio) standard. Philips had already developed commercial laserdisc
players, and Sony had a decade of digital recording research under its belt. The two com-
panies were poised for a battle—the introduction of potentially incompatible audio laser
disc formats—when instead they came to terms on an agreement to formulate a single
industry-standard digital audio technology.
Philips contributed most of the physical design, which was similar to the laserdisc format
ithadpreviously created withregardstousingpitsandlandsonthediskthat arereadbya
laser. Sony contributed the digital-to-analog circuitry, and especially the digital encoding
and error-correction code designs.
In 1980, the companies announced the CD-DA standard, which has since been referred to
as the Red Book format (so named because the cover of the published document was red).
The Red Book included the specifications for recording, sampling, and—above all—the
120mm (4.72-inch) diameter physical format you live with today. This size was chosen,
legend has it, because it could contain all of Beethoven's approximately 70-minute Ninth
Symphony without interruption, compared to 23 minutes per side of the then-mainstream
33-rpm LP record.