DVD was originally used as an initialism for the unofficial term digital videodisk.
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVD originally stood for Digital Versatile Disk, or Digital Video Disk. The acronym was dropped after DVD proved to have more uses than just storing video content. DVDs offer higher storage capacity than Compact Discs while having the same dimensions.
Pre-recorded DVDs are mass-produced using molding machines that physically stamp data onto the DVD. Such discs are known as DVD-ROM, because data can only be read and not written nor erased. Blank recordable DVDs (DVD-R and DVD+R) can be recorded once using optical disc recording technologies and supported by optical disc drives and DVD recorders and then function as a DVD-ROM. Rewritable DVDs (DVD-RW, DVD+RW, and DVD-RAM) can be recorded and erased multiple times.
DVDs are used in DVD-Video consumer digital video format and in DVD-Audio consumer digital audio format, as well as for authoring AVCHD discs. DVDs containing other types of information may be referred to as DVD data discs.
DVD specifications created and updated by the DVD Forum are published as so-called DVD Books (e.g. DVD-ROM Book, DVD-Audio Book, DVD-Video Book, DVD-R Book, DVD-RW Book, DVD-RAM Book, DVD-AR Book, DVD-VR Book, etc.).
Some specifications for mechanical, physical and optical characteristics of DVD optical discs can be downloaded as freely available standards from the ISO website. Also, the DVD+RW Alliance publishes competing DVD specifications such as DVD+R, DVD+R DL, DVD+RW or DVD+RW DL. These DVD formats are also ISO standards.
Some of DVD specifications (e.g. for DVD-Video) are not publicly available and can be obtained only from the DVD Format/Logo Licensing Corporation for a fee of US $5000. Every subscriber must sign a non-disclosure agreement as certain information in the DVD Book is proprietary and confidential.
The DVD is made of a spiral groove read or written starting at the center. The form of the groove encodes unalterable identification data known as Media Identification Code (MID). The MID contains data such as the manufacturer and model, byte capacity, allowed data rates (also known as speed), etc.
DVD uses 650 nm wavelength laser diode light as opposed to 780 nm for CD. This permits a smaller pit to be etched on the media surface compared to CDs (0.74 µm for DVD versus 1.6 µm for CD), allowing in part for DVD‘s increased storage capacity.
HP initially developed recordable DVD media from the need to store data for backup and transport.
DVD recordables are now also used for consumer audio and video recording. Three formats were developed: DVD-R/RW, DVD+R/RW (plus), and DVD-RAM. DVD-R is available in two formats, General (650 nm) and Authoring (635 nm), where Authoring discs may be recorded with encrypted content but General discs may not.
Although most DVD writers can nowadays write the DVD+R/RW and DVD-R/RW formats (usually denoted by “DVD±RW” and/or the existence of both the DVD Forum logo and the DVD+RW Alliance logo), the “plus” and the “dash” formats use different writing specifications. Most DVD readers and players will play both kinds of discs, although older models can have trouble with the “plus” variants.
Some first generation DVD players would cause damage to DVD±R/RW/DL when attempting to read them.
Dual-layer recording (sometimes also known as double-layer recording) allows DVD-R and DVD+R discs to store significantly more data—up to 8.54 gigabytes per disc, compared with 4.7 gigabytes for single-layer discs. Along with this, DVD-DLs have slower write speeds as compared to ordinary DVDs and when played on a DVD player a slight transition can sometimes be seen between the layers. DVD-R DL was developed for the DVD Forum by Pioneer Corporation; DVD+R DL was developed for the DVD+RW Alliance by Philips and Mitsubishi Kagaku Media (MKM).
A dual-layer disc differs from its usual DVD counterpart by employing a second physical layer within the disc itself. The drive with dual-layer capability accesses the second layer by shining the laser through the first semitransparent layer. In some DVD players, the layer change can exhibit a noticeable pause, up to several seconds. This caused some viewers to worry that their dual-layer discs were damaged or defective, with the end result that studios began listing a standard message explaining the dual-layer pausing effect on all dual-layer disc packaging.
DVD recordable discs supporting this technology are backward-compatible with some existing DVD players and DVD-ROM drives. Many current DVD recorders support dual-layer technology, and the price is now comparable to that of single-layer drives, although the blank media remain more expensive. The recording speeds reached by dual-layer media are still well below those of single-layer media.
There are two modes for dual-layer orientation. With Parallel Track Path (PTP), used on DVD-ROM, both layers start at the inside diameter (ID) and end at the outside diameter (OD) with the lead-out. With Opposite Track Path (OTP), used on many Digital Video Discs, the lower layer starts at the ID and the upper layer starts at the OD, where the other layer ends; they share one lead-in and one lead-out.
Content Scramble System (CSS) is a Digital Rights Management (DRM) and encryption system employed on almost all commercially produced DVD-video discs. CSS utilizes a proprietary 40-bit stream cipher algorithm. The system was introduced around 1996 and was first compromised in 1999.
The purpose of CSS is twofold:
1. CSS prevents byte-for-byte copies of an MPEG (digital video) stream from being playable since such copies do not include the keys that are hidden on the lead-in area of the restricted DVD.
2. CSS provides a reason for manufacturers to make their devices compliant with an industry-controlled standard, since CSS scrambled discs cannot in principle be played on noncompliant devices; anyone wishing to build compliant devices must obtain a license, which contains the requirement that the rest of the DRM system (region codes, Macrovision, and user operation prohibition) be implemented.
While most CSS-decrypting software is used to play DVD videos, other pieces of software (such as DVD Decrypter, AnyDVD, DVD43, Smartripper, and DVD Shrink) can copy a DVD to a hard drive and remove Macrovision, CSS encryption, region codes and user operation prohibition.
DVD-Audio is a format for delivering high fidelity audio content on a DVD. It offers many channel configuration options (from mono to 5.1 surround sound) at various sampling frequencies (up to 24-bits/192 kHz versus CDDA’s 16-bits/44.1 kHz). Compared with the CD format, the much higher-capacity DVD format enables the inclusion of considerably more music (with respect to total running time and quantity of songs) and/or far higher audio quality (reflected by higher sampling rates and greater sample resolution, and/or additional channels for spatial sound reproduction).
Despite DVD-Audio’s superior technical specifications, there is debate as to whether the resulting audio enhancements are distinguishable in typical listening environments. DVD-Audio currently forms a niche market, probably due to the very sort of format war with rival standard SACD that DVD-Video avoided.
DVD-Audio discs employ a DRM mechanism, called Content Protection for Prerecorded Media (CPPM), developed by the 4C group (IBM, Intel, Matsushita, and Toshiba).
Although CPPM was supposed to be much harder to crack than DVD-Video’s CSS, it too was eventually cracked in 2007 with the release of the dvdcpxm tool. The subsequent release of the libdvdcpxm library (which is based on dvdcpxm) allowed for the development of open source DVD-Audio players and ripping software, such as DVD-Audio Explorer. As a result, making 1:1 copies of DVD-Audio discs is now possible with relative ease, much like DVD-Video discs.
The Holographic Versatile Disc (HVD) is an optical disc technology that may one day hold up to 6 terabytes of information, although the current maximum is 500 GB. It employs a technique known as collinear holography.
The 5D DVD, being developed in the Swinburne University of Technology in Melbourne, Australia, uses a multilaser system to encode and read data on multiple layers. Technology could be compatible with current DVD disc-drive technology. Disc capacities are estimated at up to 10 terabytes, and the technology could be commercially ready by 2019.
Durability of DVDs is measured by how long the data may be read from the disc, assuming compatible devices exist that can read it: that is, how long the disc can be stored until data is lost. Five factors affect durability: sealing method, reflective layer, organic dye makeup, where it was manufactured, and storage practices.
The longevity of the ability to read from a DVD+R or DVD-R is largely dependent on manufacturing quality, ranging from 2 to 15 years, and is believed to be an unreliable medium for backup unless great care is taken for storage conditions and handling.
|Drive speed||Data rate||~Write time (min)|
|DVD-R||SS SL (1.0)||1||1||12||3.95||3.68|
|DVD-R||SS SL (2.0)||1||1||12||4.70||4.37|
|DVD-RAM||SS SL (1.0)||1||1||12||2.58||2.40|
|DVD-RAM||SS SL (2.0)||1||1||12||4.70||4.37|
|DVD-RAM||DS SL (1.0)||2||2||12||5.16||4.80|
|DVD-RAM||DS SL (2.0)||2||2||12||9.40||8.75*|