Hardware Reference
In-Depth Information
as CD, with the main difference being higher density. The DVD standard dramatically in-
creases the storage capacity of, and therefore the useful applications for, CD-sized discs.
A CD can hold a maximum of about 737MB (80-minute disc) of data, which might sound
likealotbutissimplynotenoughformanyapplications,especiallywheretheuseofvideo
is concerned. DVDs, on the other hand, can hold up to 4.7GB (single layer) or 8.5GB
(dual layer) on a single side of the disc, which is more than 11 1/2 times greater than a
CD. Double-sided DVDs can hold up to twice that amount, although you currently must
manually flip the disc over to read the other side.
Up to two layers of information can be recorded to DVDs, with an initial storage capacity
of 4.7GB of digital information on a single-sided, single-layer disc—a disc that is the
same overall diameter and thickness of a current CD. With Moving Picture Experts
Group standard 2 (MPEG-2) compression, that's enough to contain approximately 133
minutes of video, which is enough for a full-length, full-screen, full-motion feature
film—including three channels of CD-quality audio and four channels of subtitles. Using
bothlayers,asingle-sideddisccouldeasilyhold240minutesofvideoormore.Thisinitial
capacity is no coincidence; the creation of DVD was driven by the film industry, which
has long sought a storage medium cheaper and more durable than videotape.
Note
It is important to know the difference between the DVD-Video and DVD-ROM standards.
DVD-VideodiscscontainonlyvideoprogramsandareintendedtobeplayedinaDVDplay-
er connected to a television and possibly an audio system. DVD-ROM is a data-storage me-
dium intended for use by PCs and other types of computers. The distinction is similar to that
between anaudio CD andaCD-ROM. Computers might becapable ofplaying audio CDs as
wellasCD-ROMs,butdedicated audioCDplayerscan'tuseaCD-ROM'sdatatracks.Like-
wise, computer DVD drives can play DVD-Video discs (with MPEG-2 decoding in either
hardwareorsoftware),butDVD-Videoplayerscan'taccessdataonaDVD-ROM.Thisisthe
reason you must select the type of DVD you are trying to create when you make a writable
or rewritable DVD.
The initial application for DVDs was as an upgrade for CDs as well as a replacement
for prerecorded videotapes. As with CDs, which initially were designed only for music,
DVDs have since developed into a wider range of uses, including video rental, computer
data storage, and high-quality audio.
DVD History
DVD had a somewhat rocky start. During 1995, two competing standards for high-capa-
city CD drives were being developed to compete with each other for future market share.
One standard, called Multimedia CD, was introduced and backed by Philips and Sony,
