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What is DVD?
An Overview of DVD Technology
DVD is a high-density optical disc format designed for the playback of large amounts of data.
DVD originally stood for digital versatile disc or digital videodisc, but is now just known as DVD.
At first glance, a DVD disc looks much like its CD-ROM counterpart, and in fact there are several similarities.
Both share the same 120mm-diameter dimension, are 1.2mm thick plastic discs and rely on lasers to read data,
but that's where the similarities end.
A CD can hold 650MB, while a single-layer DVD disc can hold 4.7GB -
the equivalent of a two-hour digital movie or seven times the capacity of today's CD-ROMs.
Double-sided, double-layer DVD discs can store up to 17GB of data, or the equivalent of 25 CD-ROMs.
Because DVD is a digital technology, users also can be assured of little or no degeneration of their data -
unlike a well-worn VHS tape or vinyl record.
Consumers can depend on a high degree of investment protection and backward compatibility.
The Evolution of DVD
In the early 1990s, several companies began working to further the development of CD technology.
Their mission was to create a disc of similar size but much greater capacity.
These companies included Toshiba, Time Warner, Sony and Philips.
A group of computer and entertainment companies insisted that the DVD proponents agree on single standard,
and the DVD Consortium was formed.
The Consortium consisted of 10 founding companies: Hitachi, JVC, Matsushita, Mitsubishi, Philips, Pioneer, Sony, Thomson, Time Warner, and Toshiba.
To avoid a confusing and costly repeat of the VHS vs. BetaMax videotape battle,
the Consortium announced their combined DVD format in September of 1995.
Working groups with representatives from many other companies also contributed.
In May 1997, the DVD Forum replaced the Consortium.
Today, the DVD Forum consists of more than 100 companies.
DVD: Fulfilling the Needs of Two Different Industries
In developing the new standard, it was extremely important to satisfy two key business sectors:
the computer industry and Hollywood movie studios.
Both wanted a small-disc solution that guaranteed CD compatibility.
In addition, Hollywood also had its heart set on 135 minutes of storage, enough for a whole movie to be viewed without changing to a second disc.
DVD also had to meet the following requirements outlined by these two groups:
- A single, interchangeable standard for both TV and PC-based applications
- Forward compatibility with future read/write and write-once DVD discs
- A low-cost format
- No mandatory container
- Reliable data storage and retrieval
- High online capacity (133 minutes of MPEG-2 video on a single side)
- High performance for sequential and non-sequential data
- Superior picture quality comparable to laser discs
- Exceptional digital surround sound for dynamic ambiance
- Dubbing in at least three languages and subtitling in four languages
Standards Are Key
Today, because DVD is based on standards,
it achieves backward compatibility with existing compact discs without any significant
increase in the cost of a DVD player or drive.
There are currently six DVD format books published by the DVD Forum that include specifications for the following formats:
DVD-ROM: DVD-ROM drives playback DVD read-only media for desktop, notebook and ultraportable PCs.
DVD-ROM drives are being incorporated into most PCs purchased today, but can also be added as a peripheral via an upgrade kit.
With MPEG-2 and Dolby Digital Surround Sound playback capabilities, DVD-ROM drives are ideal for full-length feature films and computer games with advanced graphics.
DVD is one of the most important components of emerging "living room" computers, or PC-TVs, with large, TV-like monitors and game console-style remote control devices.
Because of its high capacity and throughput, DVD-ROM is also ideal for environments needing access to large amounts of data.
DVD-RAM: DVD-RAM drives provide all the benefits of DVD-ROM with the added advantage of rewritability.
DVD-RAM is perfectly suited for applications such as data back up, document archiving, multimedia titles and presentations.
It allows users to record and re-record from 2.6GB to 5.2GB on one disc.
DVD-RAM utilizes phase change technology, in which a laser heats the inner surface of the disc for a magnetic charge,
allowing data stored on DVD-RAM discs to be written and re-written hundreds of thousands of times.
DVD-RAM is currently shipping and is projected to be the storage medium of the future because of its storage capacity,
low-cost per MB and compatibility with other DVD formats.
DVD-R: DVD-R is a high capacity, high throughput, write-once optical disc.
It is analogous to CD-R, and is used primarily for authoring and testing DVD titles,
as well as limited distribution DVD publishing. Single-sided DVD-R discs store 3.9GB of data.
DVD-RW: Also known as DVD-Rewritable, DVD-RW is a rewritable version of DVD-R.
Offering 4.7GB capacity per disc, it is designed as an authoring tool as well as for archiving data.
DVD-RW uses DVD-R media, but is rewriteable up to 1,000 times.
DVD-RW differs from DVD-RAM in that it records data sequentially, whereas DVD-RAM provides random access to recorded data.
DVD-Audio: DVD-Audio defines a read-only optical disc designed for the playback of high-quality audio.
Supporting a wide range of digital audio options, DVD-Audio products offer consumers a superior listening experience.
DVD-Video: DVD-Video offers a high capacity, read-only format for the interactive playback of high quality video,
audio and graphics ideal for set-top box applications.
In addition to the six formats supported by the DVD Forum, DVD+RW, also known as DVD rewritable,
is another rewritable standard endorsed by the members of the Yokohama Group.
DVD+RW discs hold 3GB per side, and are designed for the same applications as DVD-RW.
Proponents of the DVD+RW format have promised the first products will be available at the end of 1999.
The Technology Behind DVD and Latest Technical Advances
The three major technological advancements that allow for the increased data capacity on a DVD are an improved laser,
disc improvements and dual-layer recording capability.
Advanced Laser Enables Greater Data Capacity
The advanced laser technology in a DVD drive produces a shorter wavelength beam of light
that allows the laser to focus in on a very small area of recorded data.
This allows the pits on the DVD discs to be packed more tightly on the disc,
increasing overall capacity. On CD-ROMs, the minimum pit length is slightly more than 0.8
micrometers. On DVD, it is 0.4 micrometers.
The laser in DVD drives also aims and focuses more accurately than its CD-ROM cousin.
DVD uses a red-light laser with a wavelength of 640 nanometers that not only reads the pits
but also guides the laser on the pitch track.
Conventional CD technology utilizes an infrared laser with a wavelength of 780 nanometers.
Also, by narrowing the track pitch (the width of the track that contains the pits)
it is possible to fit more data on the disc.
In developing DVD technology, the track pitch could be reduced to 0.75 micrometers
from the 1.6 micrometers of a conventional CD-ROM - less that half the previous width.
Bonded Together Discs are Sturdier, Allow for Dual-Sided Recording
While today's CDs are 1.2mm thick, the DVD disc uses two 0.6mm discs bonded together,
which allow for double-sided recording.
Plus, the physical format of a single DVD disc also increases reliability.
The disc is now symmetrical and more resilient to changes in temperature, humidity and
other environmental conditions, making the disc less likely to warp.
DVD discs are available in four variations:
- Single-sided, single layer with 4.7GB capacity
- Double-sided, single layer with 8.5GB capacity
- Single-sided, double layer with 9.4GB capacity
- Double-sided, double layer with 17GB capacity
Dual-Layer Recording
To provide for even greater data capacity, a focusing mechanism was designed that allows
data to be recorded on two layers. To read the second layer, the reader simply focuses
the laser a little deeper into the disc, where the second layer of data is recorded.
This same focusing mechanism is part of the solution that ensures DVD drives can read
CD-ROMs, which have different track widths and pit lengths. To read CD-ROM media, a
dual lens system was developed. Different lenses must be used to achieve the optimum
focus characteristics necessary for these different standards.
The two lenses are rotated horizontally to read signals for each disc.
The Sights are Only Matched by the Sound
To many, the audio aspects of DVD are as brilliant as the video.
This is achieved through eight sound streams, which means that there are eight routes for
digital sound. And, each of the eight streams can carry a full surround sound digital channel.
The first stream can be English, the second French and the third in Japanese, and so on.
Other applications are possible as well, including visuals accompanied by the producer's
commentary and storage soundtracks. Switching between tracks can happen via the remote control,
putting more options in the hands of users.
The recommended audio and video compression technology used to create DVD applications is
the international standard MPEG-2. MPEG is the acronym for Motion Picture Expert Group.
The audio and video quality which results from MPEG-2 compression far surpasses the quality of
MPEG-1 and other compression schemes used for CD-ROM and Video CDs.
MPEG achieves its high compression rate by storing only the changes from one frame to another,
instead of each entire frame.
MPEG-2 operates at a resolution of 720 x 480 pixels and delivers full-screen, full-motion video,
a significant advancement over the "postage stamp" size video typical of CD-ROM applications.
Through MPEG-2 video compression technology and Dolby Digital Surround Sound (AC-3) audio
compression, 133 minutes of high-quality video and audio can be stored on one DVD disc and can
be viewed through either a television set or through a multimedia computer system.
With MPEG-2, DVD-ROM dramatically transforms multimedia and interactive programs through the
use of state-of-the-art digital video. Everything from the simplest edutainment program to the
most "virtually real" games provides a complete interactive experience.
What the Future Holds
Market Demand and Outlook
DVD drives are used for a diverse array of applications, and are quickly replacing CD-ROM drives
to become the standard optical storage device in the computer industry.
According to research firm Disk/Trend, shipments of DVD-ROM drives will surpass those of CD-ROM
drives in 2001 with sales growing to nearly 80 million units.
Driving the adoption of DVD drives is the growing availability of DVD titles.
At the end of 1998, several hundred DVD titles were available and by the end of 1999,
nearly 3000 will be available, according to research firm Infotech Research.
By 2002, sales of DVD titles are expected to surpass CD-ROM titles.
The Microsoft/Intel-authored "PC '99" specification requires DVD-ROM drives as a component
for home computers.
Industry experts believe that sales of DVD devices and titles will exhibit a similar growth
pattern to the one experienced by CD-ROM. DVD's backward-compatibility this also needs
to be put up front with CD-ROMs makes it an ideal replacement for CD-ROM drives.
Sales of DVD-Video, DVD-Audio and DVD-ROM devices into the consumer market are also predicted
to exhibit exponential growth over the next five years. According to research firm Advanced
Media Research, a total of 13 million homes are expected to have one or more DVD devices
before the end of the century.
DVD is expected to replace audio CD, videotape, laser disc and CD-ROM technology, becoming the
de facto standard for home entertainment and desktop computing.
In terms of technology, the DVD format was developed with a planned growth path to support
future digital standards. With the advent of new technologies such as blue lasers,
DVD-RAM will increase well beyond 4.7GB per side, and by 2005, DVD-ROM will offer 50GB per side.
Conclusion
DVD is the first standard designed specifically with the consumer and computer electronics
industries in mind. Simply put, DVD enables consumers for the first time to enjoy enhanced
video, audio and increased data storage that allow PC users to turn their PC into true
entertainment devices.
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