DVD is a family of optical discs of the same size as compact discs (CD) but of a much greater capacity due to a higher recording density.
DVD birth. DVD forum
The developers aimed at a medium which could be used equally in audio and video equipment, in computer systems, in game consoles etc. It would bring together different spheres of electronics.
First DVD stood for Digital Video Disc. But later when the DVD functions extended it meant Digital Versatile Disk.
The development of the DVD format officially started in September 1995 by a group of 10 companies: Hitachi, JVC, Matsushita, Mitsubishi, Philips, Pioneer, Sony, Thomson, Time Warner and Toshiba. A DVD forum based on this consortium was founded in May 1997. The DVD forum is an open for entry organization which today includes more than 200 members.
The overall goal of this organization is to develop and promote the DVD format, work out compatible specifications and give licences to companies in the sphere of the DVD technology. There are special workgroups working on different aspects of the DVD technology. For some specifications there are international standards established.
Important advantages of the DVD technology
Today's DVD is a widely-spread, time-proved and dynamically developing technology with a great potential.
The first DVD formats
Initially the DVD technology was primarily based on 3 formats to meet the requirements of different spheres of DVD application:
Those formats specified the discs only for reading. The information could be recorded only once - in course of production. Later new specifications allowed users to record and rewrite discs. But the major Forum participants couldn't reach an agreement on a single specification for such discs since they wanted to keep control over their own technologies. As a result, we got several competing specifications (DVD-RAM, DVD-RW, DVD+RW formats). Let's study the DVD disc formats which are developed today.
Developing DVD formats
The developers couldn't reach an agreement on a single format of recordable discs. Because of the competition there are almost no any devices that support several formats. That is why the discs recorded in one format cannot be read in devices of other recording formats. Panasonic was first to develop a drive which could work with DVD-RAM and DVD-R(G) formats (in April 2001).
Some drives can't sometimes understand a format developed after they were released. Home equipment can be designed for a particular segment of the comsumer market (DVD-Audio, DVD-Video, both formats), and it is not necessary that it ensures reading of computer discs (this is what the forum has defined). At the same time computer drives work excellently with video, audio, multimedia and other computer discs.
UDF file system
The universal MicroUDF file system adopted in 2000 was a major achievement in providing compatibility of DVD technologies. The MicroUDF file system is a DVD adapted version of the UDF system (Universal Disk Format) which is based on the ISO-13346 standard. This file system is now gradually replacing an aging ISO9660 created for CDs. But until computer devices and discs of the ISO9660 format are not done away with, there is a UDF Bridge system which is a combination of the MicroUDF and the ISO9660. Recording of Audio/Video DVD discs can be done only with the MicroUDF.
Features of the MicroUDF file system:
With the MicroUDF one DVD disc can contain video films, audio records, photos and computer files. This provides platform compatibility, i.e. a DVD disc is a universal medium for Macintosh, DOS/Windows, OS/2, and UNIX.
Various companies today make every effort to apply the blue laser technology, i. e. of a smaller wavelength. It will increase the recording density of the discs and, therefore, improve other characteristics.
Calimetrics Inc developed the ML (multilevel) technology which can 3 times increase a capacity of a standard DVD/CD disc, and it doesn't require any changes in the mechanism or optical systems of the drives. To apply this technology it is enough to mount a set of chips developed by this company. The technology uses a pit depth (up to 8 levels) as a information characteristic. TDK together with some other companies are developing a similar technology but for CD discs.
DVD Read Only formats
DVD-ROM (Digital Versatile Disc Read Only Memory)
DVD-ROM discs are meant for computer equipment. Information can be recorded only once, at the factory.
The development of DVD is very similar to that of CD and is mainly aimed at improvement of speed characteristics and at inclusion of a recording function. The first generation DVD-ROM devices used the CLV mode and read discs at 1.38 MBytes/s (it is 1x for DVD). The 2G devices could read discs at 2X (2.8 MBytes/s). Modern DVD-ROM devices (3G) uses the CAV mode (rotation management mode) and read data at 4X-6X (5.5 - 8.3 MBytes/s) and at higher speeds. Modern DVD-ROM drives support reading of almost all formats including CD.
The DVD-Video format is designed for storage and reproduction of video. This format makes possible only to read data with video players (video recorders). This specification is based on the DVD-ROM one but it provides a special data storing method different from a bitwise disc copying. Video data are recorded in course of production in an encoded form. DVD-video reproduction is possible only on consumer video players (video recorder) or on DVD drives connected to a computer. In a computer data are decoded either on a software or on a hardware level. The modern specification ensures recording of high-quality video (up to 2 hours in MPEG-2), multichannel sound accompaniment in 8 languages, different screen formats, captions in 32 languages, interactive management thru a screen menu, up to 9 angular directions of viewing films, copy protection, division of viewing video materials among regions, children access control.
This is a new generation of an audio format after CD. The specification defines a high-quality multichannel sound, supports of wide range of sound quality (16, 20, 24 bit sampling at 44.1 to 192 kHz), CD playing by DVD players, additional information (including video, text, menu, screensavers, navigation system), connection with web-sites which provide information support, extension of features in case of new technologies.
There are two versions of the DVD-Audio format: DVD-Audio which is only for audio contents and DVD-AudioV which is for sound and additional information.
Special measures have been established to protect from illegal copying.
DVD formats for multiple recording
All known specifications of rewritable DVD discs use a multiple recording technology based on the phase changing (crystalline/amorphous) of an information layer implemented by a laser of 650 (635) nm wavelength (phase-change recording). During reading a leam is reflected from an information layer to define its optical characteristics in its different phase states (the same as in recording).
Material for multiple recording
DVD discs are made of AVIST, a material developed by TDK in 1995. Its characteristics meet the requirements of the rewriting technology:
Each format has its own advantages and disadvantages which determine their ranges of application. The most wide-spread format is DVD-RAM because of cheaper drives and discs which can work with it.
DVD-RAM (Digital Versatile Disc Random Access Memory)
This is a rewritable format developed by Panasonic, Hitachi and Toshiba.
The format was approved by the DVD forum in July 1997. More than 20 computer companies tested the equipment and discs of this format during 3 months. More than 160 forum participants voted for this specification. Today this format is the most popular.
DVD-RAM drives can read all DVD-ROM drives, while DVD-ROM drives can read only third generation DVD-RAM discs which appeared in the middle of 1999.
The G1 DVD-RAM discs could contain 2.6 GBytes per side. The modern (2G) discs carry 4.7 GBytes per side or 9.4 GBytes on for a double-sided modification.
There are two types of single-sided DVD-RAM discs - in cartridge and without it. The former ones are mainly intended for home video equipment where it is important to avoid external factors in case of intensive manual use of discs. The cartridges can be openable and non-openable.
The best advantages of DVD-RAM discs is a possibility to rewrite up to 100,000 times and a error correction mechanism.
The greatest number of rewriting cycles among all DVD formats, an error correction mechanism and random disc access both in reading and in recording made this format the most effective in secondary data storage devices. An overwhelming number of devices of mass data storage - robotic DVD libraries - use exactly this technology.
DVD-RAM discs can be used for recording and reading of stream video on equipment supporting the DVD-VR specification (see below).
DVD+RW (Digital Versatile Disc ReWritable)
The DVD+RW format is promoted only by its developers - Hewlett-Packard, Mitsubishi Chemical, Philips, Ricoh, Sony and Yamaha (the DVD forum doesn't support it).
You can record on DVD+RW discs both video or sound and computer data. These discs can be rewritten about 1000 times.
The DVD+RW served a base for the DVD+RW Video Format. Equipment and discs working in this format are positioned as fully compatible with DVD-Video equipment. It means that DVD+RW discs containing video data can be played on consumer DVD equipment which was produced earlier.
Philips announced its DVD video recorder in September 2001. DVD+RW discs recorded on this equipment can also be read by usual DVD-Video players. This solution was made in response to the DVD-VR specification (see below).
DVD-RW (Digital Versatile Disc ReRecordable)
It is also known as DVD-R/W and DVD-ER.
The DVD-RW is a multiple recording format developed by Pioneer. The discs can house 4.7 GBytes per side, are produced in single-sided and double-sided modifications and can be used for storing video, audio and other data.
DVD-RW discs can be rewritten up to 1000 times. Unlike DVD+RW and DVD-RAM, DVD-RW discs can be played by DVD-ROM drives of the first generation.
TDK states that the service life of DVD-RW discs is 100 years.
DVD disc recordable formats
DVD-R (Digital Versatile Disc Recordable)
DVD-R is developed by Pioneer. Such devices were first to record DVD discs. The recording technology is similar to the CD-R one and is based on irrevisable change with a laser of spectral characteristics of an information layer covered with special organic matter.
DVD-R discs can contain both computer data, multimedia programs and video/audio information. Given to the type of recorded data such discs can be played by other devices compatible with the format, including DVD-Video players and a majority of DVD-ROM drives. Single-sided DVD-R discs can contain 4.7 or 3.95 GBytes per side. Double-sided discs carry 9.4 GBytes (4.7 GBytes per side). Currently the format doesn't support double-sided recording technology.
Their service life is estimated more than 100 years.
There are two specifications for copy protection: DVD-R(A) and DVD-R(G). These versions use a different laser wavelength in course of recording. It means that such discs can be recorded only on the equipment which corresponds to their specification. Reproduction can be implemented on any equipment with DVD-R support.
DVD-R(A) (DVD-R for Authoring) is used in professional applications. In particular, the Cutting Master Format allows using these discs for recording of original replica (pre-mastering) instead of usual DLT types.
DVD-R(G) (DVD-R for General) is used in a wider range of fields. These discs are protected from bitwise copying of information on them from other discs. This format is supported in devices of mass data storage (for example, in robotic DVD libraries developed by Pioneer).
The DVD-VR format is based on the DVD-RAM and is supported by the DVD forum. The DVD-VR format allows recording up to 2 hours of high-quality video in a real-time mode in MPEG-2 on a single-sided DVD-RAM disc of 4.7 GB capacity and provides for such functions as editing of recorded video data, recording of different types of static images etc. Electronic devices based on this format are produced by Panasonic, Toshiba, Samsung, Hitachi etc.
Table 1. DVD disc capacity
* 1 GBytes - 1 billion bytes
Table 2. Basic parameters of DVD discs of the latest modifications
CLV stands for Constant Linear Velocity
CAV stands for Constant Angular Velocity
ZCLV stands for Zone Constant Linear Velocity
Note - in some cases "+" means that reading
or writing do not contradict the DVD forum specifications but such
devices can be still unavailable on the market. "-" means that the
specification does not require reading or recording functions without
fail, but there can be devices on the market with such possibilities.
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