Etymology
The official DVD specification documents have never defined DVD. Usage in the present day varies, with DVD, Digital Video Disc, and Digital Versatile Disc being the most common.
DVD was originally used as an initialism for the unofficial term digital videodisk.
It was reported in 1995, at the time of the specification finalization, that the letters officially stood for digital versatile disc (due to non-video applications).
However, the text of the press release announcing the specification finalization only refers to the technology as "DVD," making no mention of what (if anything) the letters stood for.
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.
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."
The basic types of DVD 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 had to be changed later on to address technical challenges, so the capacity decreased.
The 12 cm type is a standard DVD, and the 8 cm variety is known as a mini-DVD. These are the same sizes as a standard CD and a mini-CD, respectively. The capacity by surface (MiB/cm²) varies from 6.92MiB/cm² in the DVD-1 to 18.0 MiB/cm² in the DVD-18.
Note: 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. 230 (or 1,073,741,824) bytes. Most computer operating systems display file sizes in gibibytes, mebibytes and kibibytes labeled as gigabyte, megabyte and kilobyte respectively.
Each DVD sector contains 2418 bytes of data, 2048 bytes of which are user data.
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 (0.74 µm for DVD versus 1.6 µm for CD) compared to CDs, allowing for a DVD's increased storage capacity. In comparison HD DVD and Blu-Ray, the successors to the DVD format, use a wavelength of 405 nm.
Writing speeds for DVD were 1×, that is 1350 kB/s (1318 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 150 KiB/s (153.6 kB/s), approximately 9 times slower.
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 (minus/dash), DVD+R/RW (plus), and DVD-RAM.