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What is
a DVD?
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A Digital Versatile
Disk — Read Only Memory, or DVD-ROM, is a media
storage disk that closely resembles a CD or compact
disk. The major difference is that the DVD-ROM is
formatted to hold far more data. A CD commonly has
a capacity of 650 megabytes, while the smallest
capacity DVD can store about seven times more data,
or 4.38 gigabytes (GB). There are various kinds
of DVDs, but the DVD-ROM refers to a read-only disk,
or a disk that cannot be written over. If you purchase
a DVD movie from the local video store, you have
a good example of a DVD-ROM. Blank DVDs with designations
like "DVD-R" and "DVD+R" are formatted, recordable
DVDs. The —R and +R refer to competing format standards,
but both will record movies, audio or other data.
A
DVD-ROM
encodes data in the form of a spiraling trail of
pits and lands separated by mere nanometers. The
trail starts at the center of the DVD-ROM and winds
around countless times until it reaches the outer
edge. In the case of a double layer disk, the trail
continues on a second layer of material. If the
disk is also double-sided, the trail of pits and
lands extends to side two.
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The DVD-ROM has replaced
the videocassette, being far more efficient and superior
in all respects. For one, a DVD-ROM stores data in digital
form, while the videocassette uses less precise analog technology.
A DVD-ROM, under normal conditions, remains error free and
consistent, regardless of the amount of times it is viewed,
while a video cassette stretches with wear and eventually
needs replacement. The DVD-ROM can also hold more information
in a higher format, and one can skip to specific scenes
without the need for fast-forwarding or rewinding. Finally,
the DVD-ROM is much more compact and easier to store, and
DVD players can double as CD players.
If purchasing a DVD player, be sure to get one that can
play all DVD-ROM formats, including double-sided
double-layered disks. For home theater systems look for
models equipped with a 192 kilohertz (kHz), 24-bit digital/analog
converter (DAC) for true Dolby theater quality. By comparison,
standard DVD players use 96 kHz, 24-bit DACs. This is still
a big improvement over CDs, however, which use 44.1 kHz,
16-bit sampling to produce audio. For this reason, people
are moving towards DVDs to store music. An audio DVD can
hold just over an hour of multi-channel music at 192 kHz,
the highest bit rate; about two hours at 96 kHz; and close
to seven hours at the standard CD sampling rate of 44.1
kHz. While cassettes, videocassettes and laser disks have
become legacy technologies, the DVD-ROM appears to be here
to stay. Recordable DVDs are available wherever music and
movies are sold, including department stores, office supply
chains and discount marts.
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