A DVD (also known as a Digital Versatile Disc or Digital Video Disc *) is an optical disc used to store digital data. The DVD has been available on the market since Toshiba first introduced the DVD Video format in Japan in November 1996, in the United States in March 1997 and in Europe in 1998. Their main uses are for video and data storage, and they are same dimensions as compact discs (CDs), but with six times the storage capacity.

There are many variations of the term DVD include DVD-ROM (read only memory) that can be read and not written, DVD-R, DVD+R can record data only once and then function as a DVD-ROM. Also there are now DVD-RW and DVD-RAM that allow you to record and erase data many times over. The wavelength used by standard lasers is 850 nm therefore the light has a red colour. Other variants have been developed including: DVD-9 and DVD Double layer and have helped the DVD market grow as the most versatile media format for Video worldwide.

The 12 cm type is a standard DVD, and the 8 cm is known as a mini-DVD. These are the same sizes as a standard CD and a mini-CD, respectively. There are also business card DVDs that are in the shape of a hockey rink or saddle.

The standard size (12cm) capacity varies with DVD-5 SS SL at 4.7Gb : DVD-9 SS DL  at 8.54Gb : DVD-10 DS SL. The mini (8cm) DVD-1 SS SL at 1.46Gb, and the shaped business cards at 350Mb.

SS = Single-sided; DS = Double-sided; SL = Single-layer; DL = Dual-layer.

* Sometimes DVDs are also referred to as DVD Data Discs.

As next-generation of High Definition optical Blu-ray Discs now become more popular in the market, the original DVD is still outselling video on the Blu-ray format, and will continue to do so for many years to come.   In 2008, Warner’s “The Dark Knight” was the top DVD title worldwide, with sales of more than 15 million units, while Universal Studios Home Entertainment’s “Mamma Mia” achieved sales of more than 13 million units worldwide.

A Quick History of the DVD

DVD was derived for the development work of many companies and many people. DVD basically evolved from CD and related technologies. Some of the early proposals for "high-density CD" were made in 1993, and these efforts gradually faded into two competing proposed formats.

The MMCD format that was backed by Sony, Philips, and others, and the SD format backed by Toshiba, Matsushita, and Time Warner.  A group of computer companies led by IBM including representatives from Apple, Microsoft, Sun, Dell, and many others (know as the Technical Working Group, or TWG) voted to boycott both formats unless the two camps agreed on a single standard format, as nobody wanted a repeat of the VHS vs. Betamax costly and ridiculous consumer market war. After many meetings and behind the scene discussions, it was announced in September of 1995, that there would be a single format.  

No single company "owns" DVD. The official specification was developed by a consortium of ten companies: Hitachi, JVC, Matsushita, Mitsubishi, Philips, Pioneer, Sony, Thomson, Time Warner, and Toshiba. Time Warner originally trademarked the DVD logo, and has since assigned it to the DVD Format/Logo Licensing Corporation as the written term "DVD" is too common to be trademarked or owned.

The DVD soon became a huge success in the video market to the detriment of VHS.

Since 2007, VHS players are no longer manufactured.

Physical Details
The compact disc is made from 1.2 mm thick, almost-pure polycarbonate
    plastic and weighs approximately 16 grams

A  The polycarbonate disc layer has the CD encoded and are stored
     as a series of tiny indentations known as “pits”.
B. A thin layer of aluminium is applied to the surface to make it reflective
     back to the laser.
C. A lacquer layer is used to prevent oxidation
D. Artwork is screen or litho printed on the top of the disc.
E. A laser beam reads the polycarbonate disc, is reflected back,
     and is read by the player.

The optical laser reads the data through the bottom of the polycarbonate layer from the centre outward. The change in height between pits and lands results in a difference in intensity in the light reflected. By measuring the intensity change with a photodiode, the data can be read from the disc.

DVDs are susceptible to damage from both daily use and environmental exposure. Pits are much closer to the label side of a disc, so that defects and dirt on the clear side can be out of focus during playback. Consequently, DVDs suffer more scratch damage on the label side whereas scratches on the clear side can be repaired by refilling them with similar refractive plastic, or by careful polishing.