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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 History of DVD
When Philips and Sony got together to develop CD, there were just the two
companies talking primarily about a replacement for the LP. Decisions about
how the system would work were carried out largely by engineers and all
went very smoothly. The specification for the CD's successor went entirely
the other way, with arguments, confusions, half-truths and Machiavellian
intrigue behind the scenes.
It all started badly with Matsushita Electric, Toshiba and the movie-makers
Time/Warner in one corner, with their Super Disc (SD) technology, and Sony
and Philips in the other, pushing their Multimedia CD (MMCD) technology.
The two disc formats were totally incompatible, creating the possibility
of a VHS/Betamax-type battle. Under pressure from the computer industry,
the major manufacturers formed a DVD Consortium to develop a single standard.
The DVD-ROM standard that resulted at the end of 1995 was a compromise between
the two technologies but relied heavily on SD. The likes of Microsoft, Intel,
Apple and IBM gave both sides a simple ultimatum: produce a single standard,
quickly, or don' t expect any support from the computer world. The major
developers, 11 in all, created an uneasy alliance under what later became
known as the DVD Forum, continuing to bicker over each element of technology
being incorporated in the final specification.
The reasons for the continued rearguard actions was simple. For every item
of original technology put into DVD, a license fee has to be paid to the
owners of the technology. These license fees may only be a few cents per
drive but when the market amounts to millions of drives a year, it is well
worth arguing over. If this didn't make matters bad enough, in waded the
movie industry.
Paranoid about losing all its DVD-Video material to universal pirating,
Hollywood first decided it wanted an anti-copying system along the same
lines as the SCMS system introduced for DAT tapes. Just as that was being
sorted out, Hollywood became aware of the possibility of a computer being
used for bit-for-bit file copying from a DVD disc to some other medium.
The consequence was an attempt to have the U.S. Congress pass legislation
similar to the Audio Home Recording Act (the draft was called 'Digital Video
Recording Act') and to insist that the computer industry be covered by the
proposed new law.
Whilst their efforts to force legislation failed, the movie studios did
succeed in forcing a deeper copy protection requirement into the DVD-Video
standard, and the resultant Content Scrambling System (CSS) was finalised
toward the end of 1996. Subsequent to this, further copy-protections systems
have been developed.
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:
DVD-5 is a single-sided single-layered disc boosting capacity seven-fold
to 4.7GB
DVD-9 is a single-sided double-layered disc offering 8.5GB
DVD-10 will be a 9.4GB dual-sided single-layered disc
DVD-18 will increase capacity to a huge 17GB on a dual-sided dual-layered
disc.
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.
Soruce: toshiba.com
The Difference Between DVD-RW
and DVD-RAM
The 2.6GB-per-side DVD-RAM is based on the pre-existing PD (Photo-optical
Disc) technology. Since only minor format changes were necessary to implement
DVD-RAM, the R & D (Research and Developement) and component manufacturing
costs which were involved to bring 2.6GB DVD-RAM to the market were minimal;
resulting in the price being much less than DVD-R (Digital Versatile Disc,
Recordable), which is a very different technology. The newer 4.7GB-per-side
DVD-RAM has the same capacity as a single-sided, single-layer DVD-ROM or
DVD-R disc, but the file management format is somewhat different, and of
course the media is of the rewritable (phase-shift) type, with a slightly
different reflectivity than DVD-ROM or DVD-R. DVD-R media discs have a capacity
of either 3.9GB (Gigabytes) or 4.7GB per side, while DVD-RAM media holds
either 2.6GB or, with the new specification, 4.7GB per side. This means
that the tracks on DVD-R and 4.7 DVD-RAM media are only about half as wide
as those on the 2.6GB DVD-RAM media.
For a DVD-R and the newer 4.7GB DVD-RAM drives to burn the half-width tracks,
it was necessary to develope new, smaller lasers. This technology is explained
on the Pioneer DVR-S201 white sheet.
The DVD-RW media has not been released as of January, 2001. DVD-RW discs
will be of the phase-shift material, and will probably be recordable in
two formats: One recorded by, and for playback in, the Pioneer DVD-RW Video
Player/Recorder set; and another format which will conform to the DVD Video
standards (for authoring with menus, etc) as recorded by the Pioneer DVD-R/RW
drive and be playable in standard DVD Video Player sets and DVD-ROM drives
with DVD Video decoders installed in the computer.
Understanding the DVD System
When you see the term "DVD", you mostly think of the DVD discs, such as
movies and games. DVD is in reality several separate but codependent systems
providing storage and DVD playback capability.
DVD Mastering
Any time that a movie, game, or other group of media has been created and
it is decided that the storage and playback format will be DVD, the mastering
process formats this data so that it can be read and decoded by DVD players.
Before formatting is complete to disc, digital video contains an extremely
large amount of stored information. Using the MPEG-2 digital video encoding
standard, digital mastering can take this information and change it to a
format much more manageable by the common DVD player. By eliminating redundancies
(elements that are almost identical), encoding eliminates over 97 percent
of the data without noticeably affecting image quality.
Digital Video Discs
A digital video disc is made up of a reflective aluminum foil encased in
a clear plastic. Data is stored on the foil as a series of tiny pits formed
in a tight spiral on the disc. The pits are formed in the foil by stamping
it with a glass master. For a double-sided disc, two halves, each with their
foil full of data, are bonded back to back.
DVD Players
DVD players consist of a disc reader, signal processor, decoder, and a microcontroller.
Each part of the player controls one phase of the decoding and displaying
process.
The reader is the physical motor which spins the disc and the laser which
reads the information from it. Unlike audio CDs, DVD readers use red light.
The digital signal processor is an integrated circuit that translates the
laser pulses back into electrical form that other parts of the decoder can
use. The digital audio/video decoder reconstitutes the compressed data on
the disc, converting it into output for computers, TV monitors, and stereo
systems.
The microcontroller translates remote control, front panel, or other software
input into commands for the audio/video decoder and the disc reader mechanism.
The microcontroller is responsible for implementing parental lockout, dialing
distributors for access codes and controlling decryption.
There is a difference between DVD-Video and DVD-ROM. DVD-Video (often simply
called DVD) holds video programs and is played in a DVD player hooked up
to a TV. DVD-ROM holds computer data and is read by a DVD-ROM drive hooked
up to a computer. The difference is similar to that between Audio CD and
CD-ROM. DVD-ROM also includes recordable variations (DVD-R, DVD-RAM, DVD-RW;3).
New computers with DVD-ROM drives can also play DVD-Videos.
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