DVD Technical Info

DVDs are made from a 0.6 mm thick disc of polycarbonate plastic coated with a much thinner (reflective) aluminium layer. Two such discs are glued together to form a 1.2 mm double-sided disc. The substrates are half as thick as a CD to make it possible to use a lens with a higher numerical aperture and therefore use smaller pits and narrower tracks.

A single-layer DVD can store 4.7GB, which is around seven times as much as a standard CD-ROM. By employing a red laser at 650 nm (previously 780 nm) wavelength and a numerical aperture of 0.6 (previously 0.45), the read-out resolution is increased by a factor 1.65. This holds for two dimensions, so that the actual physical data density increases by a factor of 3.5. DVD uses a more efficient coding method in the physical layer. CD's error correction, CIRC, is replaced by a powerful Reed-Solomon product code, RS-PC; Eight-to-Fourteen Modulation (EFM) is replaced by a more efficient version, EFMPlus, which has the same characteristics as classic EFM. The CD subcode is removed. As a result, the DVD format is 47 percent more efficient with respect to CD-ROM, which uses a "third" error correction layer.

After separating the DVD by its contents, we can distinguish following types of DVDs :

DVD-Video (containing movies (video and sound))
DVD-Audio (containing high-definition sound)
SACD (containing high-definition sound)
DVD-Data (containing data)
The disc medium can be:

DVD-ROM (read only, manufactured by a press)
DVD-R/RW (R = Recordable once, RW = ReWritable)
DVD-RAM (random access rewritable)
DVD+R/RW (R = Recordable once, RW = ReWritable)
DVD-R DL (dual layer)
DVD+R DL (double layer)

Two DVDs with different bottom sides.The disc may have one or two sides, and one or two layers of data per side; the number of sides and layers determines the disc capacity.

The disc may have one or two sides, and one or two layers of data per side; the number of sides and layers determines the disc capacity.

DVD-5: single sided, single layer, 4.7Gigabytes (GB), or 4.38 gibibytes (GiB)
DVD-9: single sided, double layer, 8.5GB (7.92GiB)
DVD-10: double sided, single layer on both sides, 9.4GB (8.75GiB)
DVD-14: double sided, double layer on one side, single layer on other, 13.3 GB (12.3 GiB)
DVD-18: double sided, double layer on both sides, 17.1GB (15.9GiB)
The capacity of a DVD-ROM can be visually determined by noting the number of data sides, and looking at the data side(s) of the disc. Double-layered sides are sometimes gold-colored, while single-layered sides are silver-colored, like a CD. One additional way to tell if a DVD contains one or two layers is to look at the center ring on the underside of the disc. If there are two barcodes, it is a dual layer disc. If there is one barcode, there is only one layer.

Each medium can contain any of the above content and can be any layer type. Double layer DVD+R discs are already on the market.

The DVD Forum created the official DVD-ROM/R/RW/RAM standards and the DVD+RW Alliance created the DVD+R/RW standards. Since DVD+R/RW discs are not technically DVDs as per the DVD Forum standards, they are not allowed to display the DVD logo; instead, they display an "RW" logo (even if it is not re-writeable, something some consider deceptive advertising). However, they are readable by most DVD drives, so they are referred to as DVD+R and DVD+RW.

The "+" (plus) and "-" (dash) are similar technical standards and are partially compatible. As of 2004, both formats are equally popular, with about half of the industry supporting "+", and the other half "-". All DVD readers are supposed to read both formats, though real-world compatibility is around 90% for both formats, with DVD-R having the best overall compatibility in independent tests. Most new DVD writers can write both formats and carry both the RW and DVD logos.

Unlike compact discs, where sound (CDDA, Red Book) is stored in a fundamentally different fashion than data (Yellow book et al.), a properly authored DVD will always contain data in the UDF filesystem.

The data transfer rate of a DVD drive is given in multiples of 1350 kB/s, which means that a drive with 16x speed designation allows a data transfer rate of 16 × 1350 = 21600 kB/s (21.09 MB/s). As CD drive speeds are given in multiples of 150kB/s, one DVD "speed" equals nine CD "speeds," so an 8x DVD drive should have a data transfer rate similar to that of a 72x CD drive. In physical rotation terms (spins per second), one DVD "speed" equals three CD "speeds," so an 8x DVD drive has the same rotational speed as 24x CD drive.

Early CD and DVD drives read data at a constant rate. The data on the disc is passed under the read head at a constant rate (Constant Linear Velocity, or CLV). As linear (meters per second) track speed grows at outer parts of the disc proportionally to the radius, the rotational speed of the disc was adjusted according to which portion of the disc was being read. Most current CD and DVD drives have a constant rotation speed (Constant Angular Velocity, or CAV). The maximum data rate specified for the drive/disc is achieved only at the end of the disc's track (discs are written from inside). The average speed of the drive therefore equals to only about 50–70% of the maximum nominated speed. While this seems a disadvantage, such drives have a lower seek time as they do not have to change the disc's speed of rotation.

DVD History

In the early 1990s two high density optical storage standards were being developed: one was the MultiMedia Compact Disc (MMCD), backed by Philips and Sony, and the other was the Super Density Disc (SD), supported by Toshiba, Time-Warner, Matsushita Electric, Hitachi, Mitsubishi Electric, Pioneer, Thomson, and JVC. IBM's president, Lou Gerstner, acting as a matchmaker, led an effort to unite the two camps behind a single standard, anticipating a repeat of the costly format war between VHS and Betamax in the 1980s.

Philips and Sony abandoned their MMCD format and agreed upon Toshiba's SD format with two modifications that are both related to the servo tracking technology. The first one was the adoption of a pit geometry that allows "push-pull" tracking, a proprietary Philips/Sony technology. The second modification was the adoption of Philips' EFMPlus. EFMPlus, created by Kees Immink, who also designed EFM, is 6% less efficient than Toshiba's SD code, which resulted in a capacity of 4.7GB instead of SD's original 5GB. The great advantage of EFMPlus is its great resilience against disc damage such as scratches and fingerprints. The result was the DVD specification Version 1.0, announced in 1995 and finalized in September 1996.

The first DVD players and discs were available in November 1996 in Japan, March 1997 in the United States, 1998 in Europe and in 1999 in Australia. The first pressed DVD was the movie Twister in 1996. The movie had the first test for 2.1 surround sound. In 1999 Independence Day was the first movie to introduce 5.1 surround sound.

By the spring of 1999 the price of a DVD player had dropped below the $300 US mark. At that point Wal-Mart began to offer DVD players for sale in its stores. When Wal-Mart began selling DVDs in their stores, DVDs represented only a small part of their video inventory; VHS tapes of movies made up the remainder.

As of 2005 the situation is now completely reversed; DVD sales make up the bulk of gross sales and VHS is a slim minority. The price of a DVD player has dropped to below the level of a typical VCR; a low-end player with reasonable quality can be purchased for under US$50 in many retail stores and many modern computers are sold with DVD-ROM drives stock. Most, but not all, movie "sets" or series have been released in box sets, as have some entire seasons or selected episode volumes of older and newer television programs.

DVD rentals first topped those of VHS during the week of June 15, 2003 (27.7M rentals DVD vs. 27.3M rentals VHS). Major U.S. retailers Circuit City and Best Buy stopped selling VHS tapes in 2002 and 2003, respectively. In June 2005, Wal-Mart and several other retailers announced plans to phase out the VHS format entirely, in favor of the more popular DVD format.

According to the Digital Entertainment Group (DEG), all DVD sales and rentals (films, television series, special interests, etc) totaled $21.2 billion in 2004. The sales portion of that was $15.5 billion. In comparison, the total 2004 US box office for theatrical rentals was $9.53 billion (per the National Association of Theater Owners or NATO). While the growth of theatrical films on DVD has cooled recently, that of television programs and music video has increased dramatically.

In 2000, Sony released its PlayStation 2 console in Japan. In addition to playing video games developed for the system it was also able to play DVD movies. This proved to be a huge selling point because the PS2 cost about the same as DVD player but could do a whole lot more. As a result, many electronic stores that normally did not carry video game consoles carried PS2s. In keeping with this tradition, Sony has announced that it will implement one of DVD's possible successors, Blu-ray, into its next PlayStation console currently known as the PlayStation 3.

Microsoft's Xbox, released a year after the PlayStation 2, also had the capability to play DVD discs with an add-on kit, cementing the DVD's place in video game consoles.

"DVD" was originally an initialism for "Digital Video Disc." Some members of the DVD Forum believe that it should stand for "Digital Versatile Disc" to reflect its widespread use for non-video applications. Toshiba, which maintains the official DVD Forum site [1], adheres to the interpretation of "Digital Versatile Disc." The DVD Forum never reached a consensus on the matter, however, and so today the official name of the format is simply "DVD"; the letters do not officially stand for anything

DVD

DVD (sometimes called "Digital Versatile Disc" or "Digital Video Disc") is an optical disc storage media format that can be used for data storage, including movies with high video and sound quality. DVDs resemble compact discs as their physical dimensions are the same (12cm in diameter) but they are encoded in a different format and at a much higher density, using the Universal Disk Format (UDF) file system. The official DVD specification is maintained by the DVD Forum.