The megabyte is a multiple of the unit byte for digital information. Its recommended unit symbol is MB; the unit prefix mega is a multiplier of 1000000 in the International System of Units. Therefore, one megabyte is one million bytes of information; this definition has been incorporated into the International System of Quantities. However, in the computer and information technology fields, several other definitions are used that arose for historical reasons of convenience. A common usage has been to designate one megabyte as 1048576bytes, a measurement that conveniently expresses the binary multiples inherent in digital computer memory architectures. However, most standards bodies have deprecated this usage in favor of a set of binary prefixes, in which this quantity is designated by the unit mebibyte. Less common is a convention that used the megabyte to mean 1000×1024 bytes; the megabyte is used to measure either 10002 bytes or 10242 bytes. The interpretation of using base 1024 originated as a compromise technical jargon for the byte multiples that needed to be expressed by the powers of 2 but lacked a convenient name.
As 1024 approximates 1000 corresponding to the SI prefix kilo-, it was a convenient term to denote the binary multiple. In 1998 the International Electrotechnical Commission proposed standards for binary prefixes requiring the use of megabyte to denote 10002 bytes and mebibyte to denote 10242 bytes. By the end of 2009, the IEC Standard had been adopted by the IEEE, EU, ISO and NIST; the term megabyte continues to be used with different meanings: Base 10 1 MB = 1000000 bytes is the definition recommended by the International System of Units and the International Electrotechnical Commission IEC. This definition is used in networking contexts and most storage media hard drives, flash-based storage, DVDs, is consistent with the other uses of the SI prefix in computing, such as CPU clock speeds or measures of performance; the Mac OS X 10.6 file manager is a notable example of this usage in software. Since Snow Leopard, file sizes are reported in decimal units. In this convention, one thousand megabytes is equal to one gigabyte, where 1 GB is one billion bytes.
Base 2 1 MB = 1048576 bytes is the definition used by Microsoft Windows in reference to computer memory, such as RAM. This definition is synonymous with the unambiguous binary prefix mebibyte. In this convention, one thousand and twenty-four megabytes is equal to one gigabyte, where 1 GB is 10243 bytes. Mixed 1 MB = 1024000 bytes is the definition used to describe the formatted capacity of the 1.44 MB 3.5-inch HD floppy disk, which has a capacity of 1474560bytes. Semiconductor memory doubles in size for each address lane added to an integrated circuit package, which favors counts that are powers of two; the capacity of a disk drive is the product of the sector size, number of sectors per track, number of tracks per side, the number of disk platters in the drive. Changes in any of these factors would not double the size. Sector sizes were set as powers of two for convenience in processing, it was a natural extension to give the capacity of a disk drive in multiples of the sector size, giving a mix of decimal and binary multiples when expressing total disk capacity.
Depending on compression methods and file format, a megabyte of data can be: a 1 megapixel bitmap image with 256 colors stored without any compression. A 4 megapixel JPEG image with normal compression. 1 minute of 128 kbit/s MP3 compressed music. 6 seconds of uncompressed CD audio. A typical English book volume in plain text format; the human genome consists of DNA representing 800 MB of data. The parts that differentiate one person from another can be compressed to 4 MB. Timeline of binary prefixes Gigabyte § Consumer confusion Historical Notes About The Cost Of Hard Drive Storage Space the megabyte International Electrotechnical Commission definitions IEC prefixes and symbols for binary multiples
Optical disc drive
In computing, an optical disc drive is a disc drive that uses laser light or electromagnetic waves within or near the visible light spectrum as part of the process of reading or writing data to or from optical discs. Some drives can only read from certain discs, but recent drives can both read and record called burners or writers. Compact discs, DVDs, Blu-ray discs are common types of optical media which can be read and recorded by such drives. Optical disc drives that are no longer in production include CD-ROM drive, CD writer drive, combo drive, DVD writer drive supporting certain recordable and rewritable DVD formats; as of 2015, DVD writer drive supporting all existing recordable and rewritable DVD formats is the most common for desktop PCs and laptops. There are the DVD-ROM drive, BD-ROM drive, Blu-ray Disc combo drive, Blu-ray Disc writer drive. Optical disc drives are an integral part of standalone appliances such as CD players, DVD players, Blu-ray disc players, DVD recorders, certain desktop video game consoles, such as Sony PlayStation 4, Microsoft Xbox One, Nintendo Wii U, Sony PlayStation 3, certain portable video game consoles, such as Sony PlayStation Portable.
They are very used in computers to read software and consumer media distributed on disc and to record discs for archival and data exchange purposes. Floppy disk drives, with capacity of 1.44 MB, have been made obsolete: optical media are cheap and have vastly higher capacity to handle the large files used since the days of floppy discs, the vast majority of computers and much consumer entertainment hardware have optical writers. USB flash drives, high-capacity and inexpensive, are suitable where read/write capability is required. Disc recording is restricted to storing files playable on consumer appliances small volumes of data for local use, data for distribution, but only on a small scale. Optical discs are used to back up small volumes of data, but backing up of entire hard drives, which as of 2015 contain many hundreds of gigabytes or multiple terabytes, is less practical. Large backups are instead made on external hard drives, as their price has dropped to a level making this viable; the first laser disc, demonstrated in 1972, was the Laservision 12-inch video disc.
The video signal was stored as an analog format like a video cassette. The first digitally recorded optical disc was a 5-inch audio compact disc in a read-only format created by Sony and Philips in 1975; the first erasable optical disc drives were announced in 1983, by Matsushita and Kokusai Denshin Denwa. Sony released the first commercial erasable and rewritable 5.25-inch optical disc drive in 1987, with dual-sided discs capable of holding 325 MB per side. The CD-ROM format was developed by Sony and Denon, introduced in 1984, as an extension of Compact Disc Digital Audio and adapted to hold any form of digital data; the CD-ROM format has a storage capacity of 650 MB. In 1984, Sony introduced a LaserDisc data storage format, with a larger data capacity of 3.28 GB. The DVD format, developed by Panasonic and Toshiba, was released in 1995, was capable of holding 4.7 GB per layer. The first Blu-Ray prototype was unveiled by Sony in October 2000, the first commercial recording device was released to market on April 10, 2003.
In January 2005, TDK announced that they had developed an ultra-hard yet thin polymer coating for Blu-ray discs. Technically Blu-ray Disc required a thinner layer for the narrower beam and shorter wavelength'blue' laser; the first BD-ROM players were shipped in mid-June 2006. The first Blu-ray Disc titles were released by Sony and MGM on June 20, 2006; the first mass-market Blu-ray Disc rewritable drive for the PC was the BWU-100A, released by Sony on July 18, 2006. The most important part of an optical disc drive is an optical path, placed in a pickup head consisting of a semiconductor laser, a lens for focusing the laser beam, photodiodes for detecting the light reflected from the disc's surface. CD-type lasers with a wavelength of 780 nm were used. For DVDs, the wavelength was reduced to 650 nm, for Blu-ray Disc this was reduced further to 405 nm. Two main servomechanisms are used, the first to maintain the proper distance between lens and disc, to ensure the laser beam is focused as a small laser spot on the disc.
The second servo moves the pickup head along the disc's radius, keeping the beam on the track, a continuous spiral data path. Optical disc media are'read' beginning at the inner radius to the outer edge. On read only media, during the manufacturing process the tracks are formed by pressing a thermoplastic resin into a glass'master' with raised'bumps' on a flat surface, creating pits and lands in the plastic disk; because the depth of the pits is one-quarter to one-sixth of the laser's wavelength, the reflected beam's phase is shifted in relation to the incoming beam, causing mutual destructive interference and reducing the reflected beam's intensity. This is detected by photodiodes. An optical disk recorder encodes dat
A CD-ROM is a pre-pressed optical compact disc that contains data. Computers can read—but not write to or erase—CD-ROMs, i.e. it is a type of read-only memory. During the 1990s, CD-ROMs were popularly used to distribute software and data for computers and fourth generation video game consoles; some CDs, called enhanced CDs, hold both computer data and audio with the latter capable of being played on a CD player, while data is only usable on a computer. The CD-ROM format was developed by Japanese company Denon in 1982, it was an extension of Compact Disc Digital Audio, adapted the format to hold any form of digital data, with a storage capacity of 553 MiB. CD-ROM was introduced by Denon and Sony at a Japanese computer show in 1984; the Yellow Book is the technical standard. One of a set of color-bound books that contain the technical specifications for all CD formats, the Yellow Book, standardized by Sony and Philips in 1983, specifies a format for discs with a maximum capacity of 650 MiB. CD-ROMs are identical in appearance to audio CDs, data are stored and retrieved in a similar manner.
Discs are made from a 1.2 mm thick disc of polycarbonate plastic, with a thin layer of aluminium to make a reflective surface. The most common size of CD-ROM is 120 mm in diameter, though the smaller Mini CD standard with an 80 mm diameter, as well as shaped compact discs in numerous non-standard sizes and molds, are available. Data is stored on the disc as a series of microscopic indentations. A laser is shone onto the reflective surface of the disc to read the pattern of lands; because the depth of the pits is one-quarter to one-sixth of the wavelength of the laser light used to read the disc, the reflected beam's phase is shifted in relation to the incoming beam, causing destructive interference and reducing the reflected beam's intensity. This is converted into binary data. Several formats are used for data stored on compact discs, known as the Rainbow Books; the Yellow Book, published in 1988, defines the specifications for CD-ROMs, standardized in 1989 as the ISO/IEC 10149 / ECMA-130 standard.
The CD-ROM standard builds on top of the original Red Book CD-DA standard for CD audio. Other standards, such as the White Book for Video CDs, further define formats based on the CD-ROM specifications; the Yellow Book itself is not available, but the standards with the corresponding content can be downloaded for free from ISO or ECMA. There are several standards that define how to structure data files on a CD-ROM. ISO 9660 defines the standard file system for a CD-ROM. ISO 13490 is an improvement on this standard which adds support for non-sequential write-once and re-writeable discs such as CD-R and CD-RW, as well as multiple sessions; the ISO 13346 standard was designed to address most of the shortcomings of ISO 9660, a subset of it evolved into the UDF format, adopted for DVDs. The bootable CD specification was issued in January 1995, to make a CD emulate a hard disk or floppy disk, is called El Torito. Data stored on CD-ROMs follows the standard CD data encoding techniques described in the Red Book specification.
This includes cross-interleaved Reed–Solomon coding, eight-to-fourteen modulation, the use of pits and lands for coding the bits into the physical surface of the CD. The structures used to group data on a CD-ROM are derived from the Red Book. Like audio CDs, a CD-ROM sector contains 2,352 bytes of user data, composed of 98 frames, each consisting of 33-bytes. Unlike audio CDs, the data stored in these sectors corresponds to any type of digital data, not audio samples encoded according to the audio CD specification. To structure and protect this data, the CD-ROM standard further defines two sector modes, Mode 1 and Mode 2, which describe two different layouts for the data inside a sector. A track inside a CD-ROM only contains sectors in the same mode, but if multiple tracks are present in a CD-ROM, each track can have its sectors in a different mode from the rest of the tracks, they can coexist with audio CD tracks as well, the case of mixed mode CDs. Both Mode 1 and 2 sectors use the first 16 bytes for header information, but differ in the remaining 2,336 bytes due to the use of error correction bytes.
Unlike an audio CD, a CD-ROM cannot rely on error concealment by interpolation. To achieve improved error correction and detection, Mode 1, used for digital data, adds a 32-bit cyclic redundancy check code for error detection, a third layer of Reed–Solomon error correction using a Reed-Solomon Product-like Code. Mode 1 therefore contains 288 bytes per sector for error detection and correction, leaving 2,048 bytes per sector available for data. Mode 2, more appropriate for image or video data, contains no additional error detection or correction bytes, having therefore 2,336 available data bytes per sector. Note that both modes, like audio CDs, still benefit from the lower layers of error correction at the frame level. Before being stored on a disc with the techniques described above, each CD-ROM sector is scrambled to prevent some problematic patterns from showing up; these scrambled sectors follow the same encoding process described in the Red Book in order to be stored
Compact disc is a digital optical disc data storage format, co-developed by Philips and Sony and released in 1982. The format was developed to store and play only sound recordings but was adapted for storage of data. Several other formats were further derived from these, including write-once audio and data storage, rewritable media, Video Compact Disc, Super Video Compact Disc, Photo CD, PictureCD, CD-i, Enhanced Music CD; the first commercially available audio CD player, the Sony CDP-101, was released October 1982 in Japan. Standard CDs have a diameter of 120 millimetres and can hold up to about 80 minutes of uncompressed audio or about 700 MiB of data; the Mini CD has various diameters ranging from 60 to 80 millimetres. At the time of the technology's introduction in 1982, a CD could store much more data than a personal computer hard drive, which would hold 10 MB. By 2010, hard drives offered as much storage space as a thousand CDs, while their prices had plummeted to commodity level. In 2004, worldwide sales of audio CDs, CD-ROMs and CD-Rs reached about 30 billion discs.
By 2007, 200 billion CDs had been sold worldwide. From the early 2000s CDs were being replaced by other forms of digital storage and distribution, with the result that by 2010 the number of audio CDs being sold in the U. S. had dropped about 50% from their peak. In 2014, revenues from digital music services matched those from physical format sales for the first time. American inventor James T. Russell has been credited with inventing the first system to record digital information on an optical transparent foil, lit from behind by a high-power halogen lamp. Russell's patent application was filed in 1966, he was granted a patent in 1970. Following litigation and Philips licensed Russell's patents in the 1980s; the compact disc is an evolution of LaserDisc technology, where a focused laser beam is used that enables the high information density required for high-quality digital audio signals. Prototypes were developed by Sony independently in the late 1970s. Although dismissed by Philips Research management as a trivial pursuit, the CD became the primary focus for Philips as the LaserDisc format struggled.
In 1979, Sony and Philips set up a joint task force of engineers to design a new digital audio disc. After a year of experimentation and discussion, the Red Book CD-DA standard was published in 1980. After their commercial release in 1982, compact discs and their players were popular. Despite costing up to $1,000, over 400,000 CD players were sold in the United States between 1983 and 1984. By 1988, CD sales in the United States surpassed those of vinyl LPs, by 1992 CD sales surpassed those of prerecorded music cassette tapes; the success of the compact disc has been credited to the cooperation between Philips and Sony, which together agreed upon and developed compatible hardware. The unified design of the compact disc allowed consumers to purchase any disc or player from any company, allowed the CD to dominate the at-home music market unchallenged. In 1974, Lou Ottens, director of the audio division of Philips, started a small group with the aim to develop an analog optical audio disc with a diameter of 20 cm and a sound quality superior to that of the vinyl record.
However, due to the unsatisfactory performance of the analog format, two Philips research engineers recommended a digital format in March 1974. In 1977, Philips established a laboratory with the mission of creating a digital audio disc; the diameter of Philips's prototype compact disc was set at 11.5 cm, the diagonal of an audio cassette. Heitaro Nakajima, who developed an early digital audio recorder within Japan's national public broadcasting organization NHK in 1970, became general manager of Sony's audio department in 1971, his team developed a digital PCM adaptor audio tape recorder using a Betamax video recorder in 1973. After this, in 1974 the leap to storing digital audio on an optical disc was made. Sony first publicly demonstrated an optical digital audio disc in September 1976. A year in September 1977, Sony showed the press a 30 cm disc that could play 60 minutes of digital audio using MFM modulation. In September 1978, the company demonstrated an optical digital audio disc with a 150-minute playing time, 44,056 Hz sampling rate, 16-bit linear resolution, cross-interleaved error correction code—specifications similar to those settled upon for the standard compact disc format in 1980.
Technical details of Sony's digital audio disc were presented during the 62nd AES Convention, held on 13–16 March 1979, in Brussels. Sony's AES technical paper was published on 1 March 1979. A week on 8 March, Philips publicly demonstrated a prototype of an optical digital audio disc at a press conference called "Philips Introduce Compact Disc" in Eindhoven, Netherlands. Sony executive Norio Ohga CEO and chairman of Sony, Heitaro Nakajima were convinced of the format's commercial potential and pushed further development despite widespread skepticism; as a result, in 1979, Sony and Philips set up a joint task force of engineers to design a new digital audio disc. Led by engineers Kees Schouhamer Immink and Toshitada Doi, the research pushed forward laser and optical disc technology. After a year of experimentation and discussion, the task force produced the Red Book CD-DA standard. First published in 1980, the stand
HD DVD is a discontinued high-density optical disc format for storing data and playback of high-definition video. Supported principally by Toshiba, HD DVD was envisioned to be the successor to the standard DVD format. On 19 February 2008, after a protracted format war with rival Blu-ray, Toshiba abandoned the format, announcing it would no longer manufacture HD DVD players and drives; the HD DVD Promotion Group was dissolved on March 28, 2008. The HD DVD physical disc specifications were still in use as the basis for the China Blue High-definition Disc called CH-DVD; because all variants except 3× DVD and HD REC employed a blue laser with a shorter wavelength, HD DVD stored about 3.2 times as much data per layer as its predecessor. In the late 1990s, commercial HDTV sets started to enter a larger market, but there was no inexpensive way to record or play back HD content. JVC's D-VHS and Sony's HDCAM formats could store that amount of data, but were neither popular nor well-known, it was well known that using lasers with shorter wavelengths would yield optical storage with higher density.
Shuji Nakamura invented practical blue laser diodes, but a lengthy patent lawsuit delayed commercial introduction. Sony started two projects applying the new diodes: UDO and DVR Blue together with Philips, a format of rewritable discs which would become Blu-ray Disc and on with Pioneer a format of read only discs; the two formats share several technologies. In February 2002, the project was announced as Blu-ray Disc, the Blu-ray Disc Association was founded by the nine initial members; the DVD Forum was split over whether to go with the more expensive blue lasers or not. Although today's Blu-ray Discs appear identical to a standard DVD, when the Blu-ray Discs were developed they required a protective caddy to avoid mis-handling by the consumer The Blu-ray Disc prototype's caddy was both expensive and physically different from DVD, posing several problems. In March 2002, the forum voted to approve a proposal endorsed by Warner Bros. and other motion picture studios that involved compressing HD content onto dual-layer DVD-9 discs.
In spite of this decision, the DVD Forum's Steering Committee announced in April that it was pursuing its own blue-laser high-definition solution. In August, Toshiba and NEC announced their competing standard Advanced Optical Disc, it was renamed to HD DVD the next year. The HD DVD Promotion Group was a group of manufacturers and media studios formed to exchange thoughts and ideas to help promote the format worldwide, its members comprised Toshiba as the Chair Company and Secretary, Memory-Tech Corporation and NEC as Vice-Chair companies, Sanyo Electric as Auditors. The HD DVD promotion group was dissolved on March 28, 2008, following Toshiba's announcement on February 19, 2008 that it would no longer develop or manufacture HD DVD players and drives. Much like the VHS vs. Betamax videotape format war during the late 1970s and early 1980s, HD DVD was competing with a rival format—in this case, Blu-ray Disc. In 2008, major content manufacturers and key retailers began withdrawing their support for the format.
In an attempt to avoid a costly format war, the Blu-ray Disc Association and DVD Forum attempted to negotiate a compromise in early 2005. One of the issues was that Blu-ray Disc companies wanted to use a Java-based platform for interactivity, while HD DVD companies wanted to use Microsoft's "iHD". Another problem was the physical formats of the discs themselves; the negotiations proceeded and stalled. On August 22, 2005, the Blu-ray Disc Association and DVD Forum announced that the negotiations to unify their standards had failed. Rumors surfaced. By the end of September that year and Intel jointly announced their support for HD DVD. Hewlett-Packard attempted to broker a compromise between the Blu-ray Disc Association and Microsoft by demanding that Blu-ray Disc use Microsoft's HDi instead of BD-J and threatening to support HD DVD instead; the Blu-ray Disc Association did not agree to HP's demands. On March 31, 2006, Toshiba released their first consumer-based HD DVD player in Japan at ¥110,000.
HD DVD was released in the United States on April 18, 2006, with players priced at $499 and $799. The first HD DVD titles were released on April 18, 2006, they were The Last Samurai, Million Dollar Baby, The Phantom of the Opera by Warner Home Video and Serenity by Universal Studios. The first independent HD film released on HD DVD was One Six Right. In December 2006 Toshiba reported that 120,000 Toshiba branded HD DVD players had been sold in the United States, along with 150,000 HD DVD add-on units for the Xbox 360. On April 17, 2007, one year after the first HD DVD titles were released, the HD DVD group reported that they had sold 100,000 dedicated HD DVD units in the United States. In the middle of 2007, the first HD DVD Recorders were released in Japan. In November 2007, the Toshiba HD-A2 was the first high definition player to be sold at a sale price of less than US$100; these closeout sales lasted less than a day each due to both limited quantities and high demand at that price po
VCDHD is an optical disc standard, similar to CD or DVD. The technology for VCDHD was invented with in: Japan, the Netherlands and Poland. Since the name of the technology is similar to the arbitrarily inferior VCD, it's marketed using the name DVHD; the capacity of a VCDHD is 4.7 GB, the same as an average single-layer DVD. According to the official site, the tests at Philips laboratories have proven the discs to be compatible with modern DVD players. With use of blue laser technology becoming available now, the capacity may be increased by up to 15 GB; the format's main advantages include: a better resistance to scratching in comparison to DVDs a thickness of 0.6 mm extreme elasticity and the resulting resistance to bending low manufacturing and production costs and time production defect levels are only about 1% the format does not require a DVD license to manufacture It works on most DVD drivesMost popular in: Russia and Poland. Blu-ray and HD-DVD Alternative.
DVD recordable and DVD rewritable are optical disc recording technologies. Both terms describe DVD optical discs that can be written to by a DVD recorder, whereas only'rewritable' discs are able to erase and rewrite data. 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 for the distribution of home video. 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 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 chance than Pressed DVDs, due to differences in the reflective properties of dye compared to the aluminum substrate of pressed discs; 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 640 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. "R" format DVDs can read arbitrarily many times. 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 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 ideal for home DVD video recorders, where it is advantageous to have a rewritable format capable of digital video data speeds, while being removable and inexpensive. Another benefit to using a rewritable disc is, if the burning process produces errors or corrupted data, it can be written over again, corrected.
The DVD-R format was developed by Pioneer in 1997. It is approved by the DVD Forum, it has broader playback compatibility than the “+” 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. 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 popular. Developed by Philips and Sony with their DVD+RW Alliance; the "plus" format uses a more reliable bi-phase modulation technique to provide'sector' address information. It was introduced after the "-" format; the DVD+R format was developed by a coalition of corporations—now known as the DVD+RW Alliance—in mid-2002. The DVD Forum 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 accepted DVD+R and DVD+RW by adding them to its list of licensable DVD products. 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 attributed to Philips, it was "finalized" in 1997 by the DVD+RW Alliance, it was abandoned until 2001, when it was revised. As of 2006, the market for recordable DVD technology shows little sign of settling down in favour of either the plus or dash formats, the result of the increasing numbers of dual-format devices that can record to both formats, it has become 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 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 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, because the two variants of the discs are written in different formats. 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