DVD recordable
DVD recordable and DVD rewritable are a collection of optical disc formats that can be written to by a DVD recorder and by computers using a DVD writer. The "recordable" discs are write-once read-many media, where as "rewritable" discs are able to be erased and rewritten. Data is written to the disc by a laser, rather than the data being "pressed" onto the disc during manufacture, like a DVD-ROM. Pressing is used in mass production, primarily for the distribution of home video.
DVD±R is a shorthand term for both DVD+R and DVD-R formats. Likewise, the term DVD±RW refers to both rewritable disc types, the DVD+RW and the DVD-RW. DVD±R/W handles all common writable disc types, but not DVD-RAM. A drive that supports writing to all these disc types including DVD-RAM is referred to as a "Multi" recorder.
Like CD-Rs, DVD recordable uses dye to store the data. During the burning of a single bit, the laser's intensity affects the reflective properties of the burned dye. By varying the laser intensity quickly, high density data is written in precise tracks. Since written tracks are made of darkened dye, the data side of a recordable DVD has a distinct color. Burned DVDs have a higher failure-to-read rate than pressed DVDs, due to differences in the reflective properties of dye compared to the aluminum substrate of pressed discs.
Comparing recordable CDs and DVDs
The larger storage capacity of a DVD-R compared to a CD-R is achieved by focusing the laser to a smaller point, creating smaller 'pits' as well as a finer track pitch of the groove spiral which guides the laser beam. These two changes allow more pits to be written in the same physical disc area, giving higher data density. The smaller focus is possible with a shorter wavelength 'red' laser of 650 nm, compared to CD-R's wavelength of 780 nm. This is used in conjunction with a higher numerical aperture lens. The dyes used in each case are different as they are optimized for different wavelengths.R and RW formats
"R" format DVDs can be written once and read arbitrarily many times, whereas "RW" formats can be written to repeatedly. Thus, "R" format discs are only suited to non-volatile data storage, such as audio or video. This can cause confusion because the 'DVD+RW Alliance' logo is a stylized 'RW'. Thus, many discs have the RW logo, but are not rewritable.According to Pioneer, DVD-RW discs may be written to about 1,000 times before needing replacement. RW discs are used to store volatile data, such as when creating backups or collections of files which are subject to change and re-writes. They are also ideal for home DVD video recorders, where it is advantageous to have a rewritable format capable of digital video data speeds, while being removable, small, and relatively inexpensive. Another benefit to using a rewritable disc is if the burning process produces errors or corrupted data, it can simply be written over again to correct the error, or the corrupted data can be erased. This is also useful for testing optical disc authoring software.
DVD-R and DVD-RW (DVD "dash")
The DVD-R format was developed by Pioneer in 1997. It is supported by most normal DVD players and is approved by the DVD Forum. It has broader playback compatibility than DVD+R, especially with much older players. The dash format uses a "land pre-pit" method to provide sector address information.DVD "minus" R is not correct, according to DVD-R consortium recommendations; it is, in fact, a dash. DVD-R and DVD+R technologies are not directly compatible, which created a format war in the DVD technology industry. To reconcile the two competing formats, manufacturers created hybrid drives that could read both—most hybrid drives that handle both formats are labeled DVD±R and Super Multi and are very popular.
DVD-RW versions
A DVD-RW disc is a rewritable optical disc with equal storage capacity to a DVD-R, typically 4.7 GB. The format was developed by Pioneer in November 1999 and has been approved by the DVD Forum. The smaller Mini DVD-RW holds 1.46 GB, with a diameter of 8 cm.The primary advantage of DVD-RW over DVD-R is the ability to erase and rewrite to a DVD-RW disc. According to Pioneer, DVD-RW discs may be written to about 1,000 times before needing replacement.
There are three revisions of DVD-RW known as Version 1.0, Version 1.1 and Version 1.2.
The writing of DVD-RW Version 1.2 is not backwards-compatible with earlier optical drives that have only been adapted to Version 1.1 and Version 1.0.
DVD-RW media exists in the recording speed variants of 1×, 2×, 4× and 6×. Higher speed variants, although compatible with lower writing speeds, are written to with the lowest error rate at the rated speed, similarly to CD-RW.
DVD+R and DVD+RW (DVD "plus")
History
The DVD+R format was developed by a coalition of corporations—now known as the DVD+RW Alliance—in mid-2002, stemming from a research project at Hewlett-Packard Laboratories that originated in 1996. The project was the brainchild of Josh Hogan, who represented HP and was involved in the negotiations that resulted in the compromise format for DVD-ROM between the DVD Forum and the Sony and Philips teams. HP chose to partner with Sony and Philips, who were initially lukewarm to a fully rewritable format. The success of the HP Labs project in proving out the technology convinced Sony and Philips to go ahead with the move.The issue was drop-in compatibility of a rewritable format with the existing DVD-ROM players. Rewritable media have edit gaps between sectors, to provide a buffer so that any timing inaccuracies in the write clock would not result in new data accidentally overwriting any of the other sectors. DVD-ROM disks, being mastered with a continuous stream of data, had no need for edit gaps. In fact, makers of pre-recorded DVD media were quite cool to the idea of users being able to use this format for their own recordings. HP saw this as an opportunity to enter the business, but solving the lack of edit gaps was the key problem. In early 1996, HP exited the hard disk drive business, and two HPL engineers, Daniel Abramovitch and Terril Hurst, were moved onto the rewritable DVD project. Abramovitch was a servo engineer with an interest in timing loops. Reading about the wobble grooves on older optical disk formats, Abramovitch proposed that a wobble frequency at roughly the same frequency as the data frequency would provide enough timing accuracy so as to provide sub-bit accuracy on the timing. In a servo systems parlance, this was a high frequency, high-fidelity reference signal for the timing servo loop to follow. Essentially, it would be possible to turn a tracking loop sideways and use all the tools of control theory to improve the timing. The issue was that it was not clear that such a signal would not affect the data itself. It was an insight by David Towner, an optical engineer attached to the project, that the detection modes for the wobble and the data, would themselves provide enough common mode rejection to separate the signals. At this point, the notion of high frequency wobbles was born. Much of the team's effort after that was to prove out this concept, which led to the fundamental patent for the format by Abramovitch and Towner, entitled Re-Writable Optical Disk Having Reference Clock Information Permanently Formed on the Disk. By late 1998, through the monthly meetings led by project leader Carl Taussig and often accompanied by Josh Hogan, Sony and Philips had warmed to the idea of the format.
In 1999, the team had argued to then HP CEO Lew Platt that HP needed to produce products in the set-top market, the computer market, and the camcorder market to truly exploit the invention. Platt, who had a reputation of being risk averse, chose to stick with only the computer drive product scheduled for development at the Boise facility. In 2000, HP was under the direction of new CEO Carly Fiorina, and the division, under new cost constraints, chose to abandon the manufacture of any new optical drives. However, since HP owned the fundamental patent above, they could receive licensing fees for the patent itself and pursued several expansions of the patent in US Patent # 7701836. There was also US Patent # RE41881, a reissue of US Patent # 6046968 with expanded claims. Finally, there was US Patent # RE43788, a second reissue of Patent # 6046968 with more claims.
With the timing issue solved by high frequency wobbles, the other key issue solved by the HPL team was writing bits in a way that would not result in a bleeding of one bit into the next one. Because DVD+RW used phase-change media, this was solved by high speed modulation of short laser pulses to take advantage of the nonlinear heating and cooling properties of the material and control the pulse shapes. Several papers describing these efforts can be found at:
The DVD Forum initially did not approve of the DVD+R format and claimed that the DVD+R format was not an official DVD format until January 25, 2008.
On 25 January 2008, DVD6C officially accepted DVD+R and DVD+RW by adding them to its list of licensable DVD products.
Features
DVD+RW supports a method of writing called "lossless linking", which makes it suitable for random access and improves compatibility with DVD players. The rewritable DVD+RW standard was formalized earlier than the non-rewritable DVD+R. Although credit for developing the standard is often attributed to Philips, the fundamental work was done by a team at Hewlett-Packard Labs. It was "finalized" in 1997 by the DVD+RW Alliance once the fundamental patent had been filed by the HPL team. It was then abandoned until 2001, when it was heavily revised.The simulated recording mode feature is no longer an official part of the standard like it was for CD-R, CD-RW, DVD-R and DVD-RW, although supported by Plextor optical drives.
Another distinction in comparison to DVD-R/RW/R DL is that the recorder information is not written automatically to DVD+ discs by the drive. Nero DiscSpeed allows proprietarily adding such information for later retrieval.
Other changes include the removal of a dedicated SCSI erase command in optical drives, which is done by the software instead that overwrites data with null characters. This means that the standard does not allow reverting the disc to a blank state after the first write.
DVD+RW DL was once developed and announced by JVC but it was never sold due to issues with its low reflectivity.
As of 2006, the market for recordable DVD technology showed little sign of settling down in favour of either the "plus" or "dash" formats, which is mostly the result of the increasing numbers of dual-format devices that can record to both formats, known as DVD Multi Recorders. It has become very difficult to find new computer drives that can only record to one of the formats. By contrast, DVD Video recorders still favour one format over the other, often providing restrictions on what the unfavoured format will do. However, because the DVD-R format has been in use since 1997, it has had a five-year lead on DVD+R. As such, older or cheaper DVD players are more likely to favour the DVD-R standard exclusively.
DVD+R discs must be formatted before being recorded by a compatible DVD video recorder. DVD-R do not have to be formatted before being recorded by a compatible DVD video recorder,.
There are a number of significant technical differences between the "dash" and the "plus" format, although most users would not notice the difference. One example is that the DVD+R style address in pregroove system of tracking and speed control is less susceptible to interference and error, which makes the ADIP system more accurate at higher speeds than the land pre pit system used by DVD-R. In addition, DVD+R has a more robust error-management system than DVD-R, allowing for more accurate burning to media, independent of the quality of the media. The practical upshot is that a DVD+R writer is able to locate data on the disc to byte accuracy whereas DVD-R is incapable of such precision.
DVD+R also has a larger Power Calibration Area. The PCA in DVD+R has a length of 32768 sectors, compared to the 7088 of DVD-R. In the PCA, which is located close to the inner edge of the disc, a 15-step procedure is carried out to calibrate the disc drive's laser before every and during writing, to allow for small differences between discs and drives. This process is known as a power test. Calibration during writing allows for small changes in quality between different sections of the disc, such as slightly different optical properties, impurities or dye layer thickness in either the plastic or dye. The results of the power tests are stored in a Recording Management Area, which can hold up to 7,088 calibrations. The disc can not be written to after the RMA becomes full, although it may be emptied in RW discs. CD-R, CD-RW, DVD-R, DVD+R, DVD-R DL, DVD+R DL, and DVD+RW all have a PCA. CDs may also have two PCAs: one on the inner edge of the disc, for low speed testing, and another on the outer edge for high speed testing.
Additional session linking methods are more accurate with DVD+R versus DVD-R, resulting in fewer damaged or unusable discs due to buffer under-run and multi-session discs with fewer PI/PO errors.
Like other "plus" media, it is possible to change the book type to increase the compatibility of DVD+R media. This is also known as bitsetting.