HD DVD

HD DVD (short for High Definition/Density Digital Versatile/Video Disc) is a discontinued high-density optical disc format for storing data and 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 develop or manufacture HD DVD players and drives. The HD DVD Promotion Group was dissolved on March 28, 2008.

The HD DVD physical disc specifications (but not the codecs) were still in use as the basis for the China Blue High-definition Disc (CBHD) formerly 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 (maximum capacity: 15 GB per layer compared to 4.7 GB per layer).

History

In the mid 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.

DVD-R

DVD-R is a digital optical disc storage format. A DVD-R is a DVD that can be written once and read arbitrarily many times.

A DVD-R typically has a storage capacity of 4.7 GB. Pioneer has also developed an 8.5 GB dual layer version, DVD-R DL, which appeared on the market in 2005.

DVD-R(W) is one of three competing industry standard DVD recordable formats; the others are DVD+R(W) and DVD-RAM. A DVD-R can be written only once, in contrast with a rewritable DVD formats such as DVD-RW or DVD+RW which can be rewritten multiple (1000+) times.

History

The DVD-R format was developed by Pioneer in 1997. It is supported by most normal DVD players and is approved by the DVD Forum.

Technical specifications

The larger storage capacity of a DVD-R compared to a CD-R is achieved through smaller pit size and smaller track pitch of the groove spiral which guides the laser beam. Consequently, more pits can be written on the same physical sized disc. In order to write smaller pits onto the recording dye layer, a red laser beam with a wavelength of 640 nm (for general use recordable DVD, versus a wavelength of 780 nm for CD-R) is used in conjunction with a higher numerical aperture lens. Because of this shorter wavelength, DVD-R and DVD+R use different dyes from CD-R to properly absorb this wavelength.

DVD+R

DVD+R is a digital optical disc storage format. A DVD+R is a DVD that can be written once and read arbitrarily many times.

A DVD+R disc holds 4.7 GB of storage, generally used for non-volatile data storage or video applications.

The DVD+R format is similar to, but not compatible with, the older DVD-R format.

A DVD+R can be written only once, in contrast with a rewritable DVD formats such as DVD-RW or DVD+RW which can be rewritten multiple (1000+) times.

History

The DVD+R format was developed by a coalition of corporations—now known as the DVD+RW Alliance—in mid-2002 (though most of the initial advocacy was from Sony). The DVD+R format competes with the DVD-R format, which is developed by the DVD Forum. The DVD Forum initially 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.

In October 2003, it was demonstrated that double layer technology could be used with a DVD+R disc to nearly double the capacity to 8.5 GB per disc. Manufacturers have incorporated this technology into commercial devices since mid-2004.

DVD±R

DVD±R (also DVD+/-R, or "DVD plus/dash R") is not a separate DVD format, but rather is a shorthand term for a DVD drive that can accept both of the common recordable DVD formats (i.e. DVD-R and DVD+R). Likewise, DVD±RW (also written as DVD±R/W, DVD±R/RW, DVD±R/±RW, DVD+/-RW, and other arbitrary ways) handles both common rewritable disc types (i.e. DVD-RW and DVD+RW, but not usually DVD-RAM).

See also

References