DVD-R read/write side |
|
| Media type | Optical disc |
|---|---|
| Capacity | 4.7 GB (single-sided, single-layer – common) 8.5–8.7 GB (single-sided, double-layer) 9.4 GB (double-sided, single-layer) 17.08 GB (double-sided, double-layer – rare) |
| Read mechanism | 650 nm laser, 10.5 Mbit/s (1×) |
| Write mechanism | 10.5 Mbit/s (1×) |
| Standard | DVD Forum's DVD Books[1][2][3] and DVD+RW Alliance specifications |
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. 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.
Contents |
Before the advent of DVD and Blu-ray, Video CD (VCD) became the first format for distributing digitally encoded films on standard 120 mm optical discs. (Its predecessor, CD Video, used analog video encoding.) VCD was on the market in 1993.[4] In the same year, two new optical disc storage formats were being developed. One was the Multimedia Compact Disc (MMCD), backed by Philips and Sony, and the other was the Super Density (SD) disc, supported by Toshiba, Time Warner, Matsushita Electric, Hitachi, Mitsubishi Electric, Pioneer, Thomson, and JVC.
Regarding writable media, long before the invention of even CD-R, optical Write Once Read Many (WORM) drives were used that used 12" disks in a cartridge. These WORM disks used an ablative technology to store data.
Representatives of the SD camp approached IBM, asking for advice on the file system to use for their disc as well as seeking support for their format for storing computer data. Alan E. Bell, a researcher from IBM's Almaden Research Center got that request and also learned of the MMCD development project. Wary of being caught in a repeat of the costly videotape format war between VHS and Betamax in the 1980s, he convened a group of computer industry experts, including representatives from Apple, Microsoft, Sun, Dell, and many others. This group was referred to as the Technical Working Group, or TWG.
The TWG voted to boycott both formats unless the two camps agreed on a single, converged standard.[5] Lou Gerstner, president of IBM, was recruited to apply pressure on the executives of the warring factions. Eventually, the computer companies won the day, and a single format, now called DVD, was agreed upon. The TWG also collaborated with the Optical Storage Technology Association (OSTA) on the use of their implementation of the ISO-13346 file system (known as Universal Disc Format) for use on the new DVDs.
Philips and Sony decided it was in their best interest to avoid another format war over their Multimedia Compact Disc, and agreed to unify with companies backing the Super Density Disc to release a single format with technologies from both. The specification was mostly similar to Toshiba and Matsushita's Super Density Disc, except for the dual-layer option (MMCD was single-sided and optionally dual-layer, whereas SD was single-layer but optionally double-sided) and EFMPlus modulation.
EFMPlus was chosen because of its great resilience to disc damage, such as scratches and fingerprints. EFMPlus, created by Kees Immink (who also designed EFM), is 6% less efficient than the modulation technique originally used by Toshiba, which resulted in a capacity of 4.7 GB, as opposed to the original 5 GB. The result was the DVD specification, finalized for the DVD movie player and DVD-ROM computer applications in December 1995.
The DVD Video format was first introduced by Toshiba in Japan in November 1996, in the United States in March 1997 (test marketed),[6] in Europe in October 1998, and in Australia in February 1999.
In May 1997, the DVD Consortium was replaced by the DVD Forum, which is open to all other companies.[6]
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.).[1][2][3]
Some specifications for mechanical, physical and optical characteristics of DVD optical discs can be downloaded as freely available standards from the ISO website.[7] 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.[8][9][10][11]
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.[12][13] Every subscriber must sign a non-disclosure agreement as certain information in the DVD Book is proprietary and confidential.[12]
The official DVD charter documents specify that the basis of the DVD name stems from the term digital versatile disc.[14] Usage in the present day varies, with Digital Versatile Disc,[15] Digital Video Disc, and DVD being the most common.
DVD was originally used as an initialism for the unofficial term digital videodisc.[16]
A newsgroup FAQ written by Jim Taylor (a prominent figure in the industry) claims that four years later, in 1999, the DVD Forum stated that the format name was simply the three letters "DVD" and did not stand for anything.[17]
The DVD Forum website has a section called "DVD Primer" in which the answer to the question, "What does DVD mean?" reads, "The keyword is 'versatile.' Digital Versatile Discs provide superb video, audio and data storage and access—all on one disc."[18]
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 pre-recorded information as to who really manufactures the disc, under a certain brand name that the consumer is more familiar with. Also included is the byte capacity and permitted burning speeds (dependent on both the recorder, or burner, as well as what the disc can handle). This information can be read on many disc authoring software, such as ImgBurn.
A MID code is generally seen to be more reassuring for individuals whose priority is the long term storage of their data than just a buying for brand name sake. However, not all MID codes are produced in the same way. For example internet club Club MyCE specialises in disc burning consensually swear that anything not produced by Japanese disc manufacturers Verbatim or Taiyo Yuden will be of inferior burning quality and offer lower longtivity than people who burn Verbatim or Taiyo Yuden discs.
This is for many reasons. Verbatim and Taiyo Yuden have high quality standards to ensure their discs are excellent, (and anything that fails their strict quality regulation often gets destroyed) whilst other famous disc manufacturers, such as CMC Magnetics Corporation or Ritek Corporation tend to produce to vary per batch, resulting in inconsistency and poor burning results. Another reason is the burner's firmware; a set of instructions varying from burner to burner as to how to interact with the disc. They determine how well a burn will be, or even if it will finish at all. A burn that fails to record during burning, or verifying, is referred to as a "coaster" - or an unusable disc. Several errors as such may be encountered when trying to play back the disc.
Additionally, it is the firmware that determines how well it supports the MID code. Samsung and BenQ burners for example tend to be more tolerant of less well known MID codes, whilst a LG and a Matsushita burner (made by parent company Panasonic) might be a little pickier over what it can handle.
As a result, many disc producers have turned to "faking" mid codes in order to obtain better firmware support. UmeDisc, who produce discs on behalf of AOne, Tesco, Signellex, etc. may turn to faking a Taiyo Yuden MID or a Mitsubishi MKM MID (manufacturer for Verbatim) so the burner can interpret it better. An AOne 8x DVD-R disc uses a Taiyo Yuden MID, (TYG02) although its real MID code should be UME01.
The cheaper brand of discs may turn to "outsourcing" their products. This is where a brand name of disc changes the manufacturer depending on who on will sell them a batch of discs at the lowest price. Memorex is quite famous for changing their manufacturers on a regular occasion, (one spindle of DVD blanks may be produced by one manufacturer whilst another spindle may be produced by another). Brands who outsource tend to obtain the lowest quality batch of spindle, and thus makes them inconsistent for long term, let alone for burning.
However, some brands of discs remain loyal to their supplier. Traxdata and Arita are Ritek-only brands, whilst Datasafe and Datawrite are firm with CMC Magnetics.
DVD was adopted by movie and home entertainment distributors to replace the ubiquitous VHS tape as the primary means of distributing films to consumers in the home entertainment marketplace. DVD was chosen for its superior ability to reproduce moving pictures and sound, for its superior durability, and for its interactivity. Interactivity had proven to be a feature which consumers, especially collectors, favored when the movie studios had released their films on LaserDisc. When the price point for a LaserDisc at approximately $100 per disc moved to $20 per disc at retail, this luxury feature became available for mass consumption. Simultaneously, the movie studios decided to change their home entertainment release model from a rental model to a for purchase model, and large numbers of DVDs were sold.
At the same time, a demand for interactive design talent and services was created. Movies in the past had uniquely designed title sequences. Suddenly every movie being released required information architecture and interactive design components that matched the film's tone and were at the quality level that Hollywood demanded for its product.
DVD as a format had two qualities at the time that were not available in any other interactive medium: enough capacity and speed to provide high quality, full motion video and sound, and low cost delivery mechanism provided by consumer products retailers. Retailers would quickly move to sell their players for under $200, and eventually for under $50 at retail. In addition, the medium itself was small enough and light enough to mail using general first class postage. Almost overnight, this created a new business opportunity and model for business innovators, such as Netflix, to re-invent the home entertainment distribution model. It also opened up the opportunity for business and product information to be inexpensively provided on full motion video through direct mail.
| Designation | Sides | Layers (total) |
Diameter (cm) |
Capacity | ||
|---|---|---|---|---|---|---|
| (GB) | (GiB) | |||||
| DVD-1[21] | SS SL | 1 | 1 | 8 | 1.46 | 1.36 |
| DVD-2 | SS DL | 1 | 2 | 8 | 2.66 | 2.47 |
| DVD-3 | DS SL | 2 | 2 | 8 | 2.92 | 2.72 |
| DVD-4 | DS DL | 2 | 4 | 8 | 5.32 | 4.95 |
| DVD-5 | SS SL | 1 | 1 | 12 | 4.70 | 4.37 |
| DVD-9 | SS DL | 1 | 2 | 12 | 8.54 | 7.95 |
| DVD-10 | DS SL | 2 | 2 | 12 | 9.40 | 8.75 |
| DVD-14[22] | DS SL+DL | 2 | 3 | 12 | 13.24 | 12.33 |
| DVD-18 | DS DL | 2 | 4 | 12 | 17.08 | 15.90 |
| Designation | Sides | Layers (total) |
Diameter (cm) |
Capacity | ||
|---|---|---|---|---|---|---|
| (GB) | (GiB) | |||||
| 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-RW | SS SL | 1 | 1 | 12 | 4.70 | 4.37 |
| DVD+R | SS SL | 1 | 1 | 12 | 4.70 | 4.37 |
| DVD+RW | SS SL | 1 | 1 | 12 | 4.70 | 4.37 |
| DVD-R | DS SL | 2 | 2 | 12 | 9.40 | 8.75 |
| DVD-RW | DS SL | 2 | 2 | 12 | 9.40 | 8.75 |
| DVD+R | DS SL | 2 | 2 | 12 | 9.40 | 8.75 |
| DVD+RW | DS SL | 2 | 2 | 12 | 9.40 | 8.75 |
| DVD-RAM | SS SL | 1 | 1 | 8 | 1.46 | 1.36* |
| DVD-RAM | DS SL | 2 | 2 | 8 | 2.65 | 2.47* |
| 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* |
The basic types of DVD (12 cm diameter, single-sided or homogeneous double-sided) are referred to by a rough approximation of their capacity in gigabytes. In draft versions of the specification, DVD-5 indeed held five gigabytes, but some parameters were changed later on as explained above, so the capacity decreased. Other formats, those with 8 cm diameter and hybrid variants, acquired similar numeric names with even larger deviation.
The 12 cm type is a standard DVD, and the 8 cm variety is known as a MiniDVD. These are the same sizes as a standard CD and a mini-CD, respectively. The capacity by surface (MiB/cm2) varies from 6.92 MiB/cm2 in the DVD-1 to 18.0 MiB/cm2 in the DVD-18.
As with hard disk drives, in the DVD realm, gigabyte and the symbol GB are usually used in the SI sense (i.e., 109, or 1,000,000,000 bytes). For distinction, gibibyte (with symbol GiB) is used (i.e., 10243 (230), or 1,073,741,824 bytes).
Each DVD sector contains 2,418 bytes of data, 2,048 bytes of which are user data. There is a small difference in storage space between + and - (hyphen) formats:
| Type | Sectors | Bytes | kB | MB | GB | KiB | MiB | GiB |
|---|---|---|---|---|---|---|---|---|
| DVD-R SL | 2,298,496 | 4,707,319,808 | 4,707,319.808 | 4,707.320 | 4.707 | 4,596,992 | 4,489.250 | 4.384 |
| DVD+R SL | 2,295,104 | 4,700,372,992 | 4,700,372.992 | 4,700.373 | 4.700 | 4,590,208 | 4,482.625 | 4.378 |
| DVD-R DL | 4,171,712 | 8,543,666,176 | 8,543,666.176 | 8,543.666 | 8.544 | 8,343,424 | 8,147.875 | 7.957 |
| DVD+R DL | 4,173,824 | 8,547,991,552 | 8,547,991.552 | 8,547.992 | 8.548 | 8,347,648 | 8,152.000 | 7.961 |
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 1.5 µm for CD), allowing in part for DVD's increased storage capacity.
In comparison, Blu-ray Disc, the successor to the DVD format, uses a wavelength of 405 nm, and one dual-layer disc has a 50 GB storage capacity.
Writing speeds for DVD were 1×, that is, 1,385 kB/s (1,353 KiB/s), in the first drives and media models. More recent models, at 18× or 20×, have 18 or 20 times that speed. Note that for CD drives, 1× means 153.6 kB/s (150 KiB/s), about one-ninth as swift.[21][23]
| Drive speed | Data rate | ~Write time (min)[24] | |||
|---|---|---|---|---|---|
| (Mbit/s) | (MB/s) | (MiB/s) | SL | DL | |
| 1× | 11.08 | 1.39 | 1.32 | 57 | 103 |
| 2× | 22.16 | 2.77 | 2.64 | 28 | 51 |
| 2.4× | 26.59 | 3.32 | 3.17 | 24 | 43 |
| 2.6× | 28.81 | 3.60 | 3.43 | 22 | 40 |
| 4× | 44.32 | 5.54 | 5.28 | 14 | 26 |
| 6× | 66.48 | 8.31 | 7.93 | 9 | 17 |
| 8× | 88.64 | 11.08 | 10.57 | 7 | 13 |
| 10× | 110.80 | 13.85 | 13.21 | 6 | 10 |
| 12× | 132.96 | 16.62 | 15.85 | 5 | 9 |
| 16× | 177.28 | 22.16 | 21.13 | 4 | 6 |
| 18× | 199.44 | 24.93 | 23.78 | 3 | 6 |
| 20× | 221.60 | 27.70 | 26.42 | 3 | 5 |
| 22× | 243.76 | 30.47 | 29.06 | 3 | 5 |
| 24× | 265.92 | 33.24 | 31.70 | 2 | 4 |
This mechanism is shown right side up; the disc would sit on top of it. The laser and optical system scans the underside of the disc.
With reference to the photo, just to the right of image center is the disc spin motor, a gray cylinder, with its gray centering hub and black resilient drive ring on top. A clamp (not in the photo, retained in the drive's cover), pulled down by a magnet, clamps the disc when this mechanism rises, after the disc tray stops moving inward. This motor has an external rotor – every visible part of it spins.
The gray metal chassis is shock-mounted at its four corners to reduce sensitivity to external shocks, and to reduce drive noise when running fast. The soft shock mount grommets are just below the brass-colored washers at the four corners (the left one is obscured). Running through those grommets are screws to fasten them to the black plastic frame that's underneath.
Two parallel precision guide rods that run between upper left and lower right in the photo carry the "sled", the moving optical read-write head. As shown, this "sled" is close to, or at the position where it reads or writes at the edge of the disc.
A dark gray disc with two holes on opposite sides has a blue lens surrounded by silver-colored metal. This is the lens that's closest to the disc; it serves to both read and write by focusing the laser light to a very small spot. Under the disc is an ingenious actuator comprising permanent magnets and coils that move the lens up and down to maintain focus on the data layer. As well, the actuator moves the lens slightly toward and away from the spin-motor spindle to keep the spot on track. Both focus and tracking are relatively quite fast and very precise.
To select tracks (or files) as well as advancing the "sled" during continuous read or write operations, a stepping motor rotates a coarse-pitch leadscrew to move the "sled" throughout its total travel range. The motor, itself, is the gray cylinder just to the left of the most-distant shock mount; its shaft is parallel to the support rods. The leadscrew, itself, is the rod with evenly-spaced darker details; these are the helical groove that engages a pin on the "sled".
The irregular orange material is flexible etched copper foil supported by thin sheet plastic; these are "flexible printed circuits" that connect everything to the electronics (which is not shown).
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 CSS encrypted video content but General discs may not.[25]
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 7.95 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).[26]
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.[27] 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.[26] 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. A potential reason is how Dual Layer discs are not as well matured compared to the Single Layer discs, as well as consumers, on a whole, have no desire for increased burning speeds.
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.
DVD-Video is a standard for storing and distributing video/audio content on DVD media. The format went on sale in Japan in 1996, in the United States in 1997, in Europe in 1998 and in Australia in 1999.[28] DVD-Video became the dominant form of home video distribution in Japan when it first went on sale in 1996, but did not become the dominant form of home video distribution in the United States until June 15, 2003, when weekly DVD-Video in the United States rentals began outnumbering weekly VHS cassette rentals, reflecting the rapid adoption rate of the technology in the U.S. marketplace.[5][29] Currently, DVD-Video is the dominant form of home video distribution worldwide, although in Japan it was surpassed by Blu-ray Disc when Blu-ray first went on sale in Japan on March 31, 2006.
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:
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.
The rise of filesharing and "piracy" has prompted many copyright holders to display notices on DVD packaging or displayed on screen when the content is played that warn consumers of the illegality of certain uses of the DVD. It is commonplace to include a 90 second advert warning that most forms of copying the contents are illegal. Many DVDs prevent skipping past or fast-forwarding through this warning.
Arrangements for renting and lending differ by geography. In the U.S., the right to re-sell, rent, or lend out bought DVDs is protected by the first-sale doctrine under the Copyright Act of 1976. In Europe, rental and lending rights are more limited, under a 1992 European Directive that gives copyright holders broader powers to restrict the commercial renting and public lending of DVD copies of their work.
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.[31] As a result, making 1:1 copies of DVD-Audio discs is now possible with relative ease, much like DVD-Video discs.
In 2006, two new formats called HD DVD and Blu-ray Disc were released as the successor to DVD. HD DVD competed unsuccessfully with Blu-ray Disc in the format war of 2006–2008. A dual layer HD DVD can store up to 30GB and a dual layer Blu-ray disc can hold up to 50GB.[32][33]
However, unlike previous format changes, e.g., audio tape to Compact Disc or VHS videotape to DVD, there is no immediate indication that production of the standard DVD will gradually wind down, as they still dominate, with around 75% of video sales and approximately one billion DVD player sales worldwide as of 3 April 2011. In fact, experts claim that the DVD will remain the dominant medium for at least another five years as Blu-ray technology is still in its introductory phase, write and read speeds being poor as well as the fact of necessary hardware being expensive and not readily available.[5][34][35]
Consumers initially were also slow to adopt Blu-ray due to the cost.[36] By 2009, 85% of stores were selling Blu-ray Discs. A high-definition television and appropriate connection cables are also required to take advantage of Blu-ray disc. Some analysts suggest that the biggest obstacle to replacing DVD is due to its installed base; a large majority of consumers are satisfied with DVDs.[37] The DVD succeeded because it offered a compelling alternative to VHS. In addition, Blu-ray players are designed to be backward-compatible, allowing older DVDs to be played since the media are physically identical; this differed from the change from vinyl to CD and from tape to DVD, which involved a complete change in physical medium. As of 2011[update] it is still commonplace for major releases to be issued in "combo pack" format, including both a DVD and a Blu-ray disc (as well as, in many cases, a third disc with an authorized digital copy). Also, some multi-disc sets use Blu-ray for the main feature, but DVDs for supplementary features (examples of this include the Harry Potter "Ultimate Edition" collections, the 2009 re-release of the 1967 The Prisoner TV series, and a 2007 collection related to Blade Runner). Another reason cited (July 2011) for the slower transition to Blu-ray from DVD is the necessity of and confusion over "firmware updates" and needing an internet connection to perform updates.
This situation can be best compared to the changeover from 78 rpm shellac recordings to 45 rpm and 33⅓ rpm vinyl recordings; because the medium used for the earlier format was virtually the same as the latter version (a disc on a turntable, played using a needle), phonographs continued to be built to play obsolete 78s for decades after the format was discontinued. Manufacturers continue to release standard DVD titles as of 2011[update], and the format remains the preferred one for the release of older television programs and films, with some programs such as Star Trek: The Original Series needing to be re-scanned to produce a high definition version from the original film recordings (certain special effects were also updated in order to be better received in high-definition viewing).[38] In the case of Doctor Who, a series primarily produced on standard definition videotape between 1963 and 1989, BBC Video reportedly intends to continue issuing DVD-format releases of that series until at least November 2013 (since there would be very little increase in visual quality from upconverting the standard definition videotape masters to high definition).[39]
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.[40]
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,[41][42][43] and is believed to be an unreliable medium for backup unless great care is taken for storage conditions and handling.
According to the Optical Storage Technology Association (OSTA), "manufacturers claim life spans ranging from 30 to 100 years for DVD, DVD-R and DVD+R discs and up to 30 years for DVD-RW, DVD+RW and DVD-RAM".[44]
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