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DVD - technical definition

(Digital VideoDisc or Digital Versatile Disc) An optical digital disc for storing movies and data. Introduced in the U.S. in 1997, and developed by both the computer and movie industries, the disc uses the same diameter platter as a CD (120mm/4.75" diameter), but holds 4.7GB rather than 700MB. Whereas CDs use only one side, DVDs can be recorded on both sides as well as in dual layers. DVD drives/players read most CD media as well. See CSS and DVD region codes.

For 2x, 4x, 8x, etc. drive specifications, see DVD drives.

Movies - Standard Definition
DVD-Video is the movie format, which uses MPEG-2 compression to provide approximately two hours of video per side at standard definition TV resolution (480i resolution). When most people mention the word "DVD," they are referring to a DVD-Video disc. See DVD-Video and DTV.

Movies - High Definition
Blu-ray is the video format that has enough storage for high-definition movies at 1080p resolution. See Blu-ray and table of capacity comparisons below.

Read-Only Data DVDs
Designed for data files, a DVD-ROM disc is a higher-capacity CD-ROM, and like CD-ROMs, DVD-ROMs are manufactured. See DVD-ROM.

Writable/Recordable Data DVDs
A DVD-RAM is a rewritable DVD that functions like a removable hard disk. DVD-RAM media can be rewritten 100,000 times before they are no longer usable. See DVD-RAM.

DVD-R and DVD+R are competing write-once formats for movies or data. DVD-RW and DVD+RW are competing rewritable (re-recordable) formats that unlike DVD-RAM's 100,000 cycles, can only be rewritten 1,000 times. Aimed at the consumer, 1,000 rewrites is considered more than sufficient. See DVD-R, DVD+R, DVD-RW and DVD+RW.

Music DVDs
DVD-Audio is a second-generation digital music format that provides higher sampling rates than audio CDs. Many welcomed the new format, believing that the original audio CD was unable to capture the total sound spectrum, but it never took off. See DVD-Audio.

DVD Stands For?

Originally, "Digital VideoDisc." Since the technology became important to the computer world, the "video" was dropped, and it was just D-V-D. Later, it was dubbed "Digital Versatile Disc" by the DVD Forum. Take your pick.

Minus (-R/-RW) and Plus (+R/+RW)

The formats endorsed by the DVD Forum (www.dvdforum.org) have a hyphen in their names and are verbalized as "DVD Minus R" or "DVD Dash R" (DVD-R) and "DVD Minus RW" or "DVD Dash RW" (DVD-RW). The competing formats from the DVD+RW Alliance (www.dvdrw.com) use a plus sign: "DVD Plus R" (DVD+R) and "DVD Plus RW" (DVD+RW). Starting in 2002, drives that supported both Minus and Plus formats were introduced. See DVD Forum and DVD+RW Alliance.

Specifications

Following are the various DVD types and capacities. Also included is the Blu-ray high-definition format (see Blu-ray). See also DTV.

 Type             Sides  Layers  Capacity

 Read Only Standard Definition
 DVD-Video/DVD-ROM  1     1       4.7GB (DVD-5)
 DVD-Video/DVD-ROM  1     2       8.5GB (DVD-9)
 DVD-Video/DVD-ROM  2     1       9.4GB (DVD-10)
 DVD-Video/DVD-ROM  2     2      17.0GB (DVD-18)

 Read Only High Definition
 Blu-ray (BD-ROM)   1     1      25.0GB
 Blu-ray (BD-ROM)   1     2      50.0GB
 Blu-ray (BD-ROM)   2     1      50.0GB

 Write Once Standard Definition
 DVD-R (A)          1     1       4.7GB
 DVD-R (G)          1     1       4.7GB
 DVD-R (G)          2     1       9.4GB
 DVD-R DL           1     2       8.5GB
 DVD+R              1     1       4.7GB
 DVD+R DL           1     2       8.5GB

 Write Once High Definition
 Blu-ray (BD-R)     1     1      25.0GB
 Blu-ray (BD-R)     1     2      50.0GB
 See Blu-ray.

 Type             Sides  Layers  Capacity

 Rewritable Standard Definition (100K cycles)
 DVD-RAM Ver. 1     1     1       2.6GB
 DVD-RAM Ver. 1     2     1       5.2GB
 DVD-RAM Ver. 2     1     1       4.7GB
 DVD-RAM Ver. 2     2     1       9.4GB
 DVD-RAM (80 mm)    1     1       1.46GB
 DVD-RAM (80 mm)    2     1       2.92GB

 Rewritable Standard Definition (1K cycles)
 (Also called "Re-recordable")
 DVD-RW             1     1       4.7GB
 DVD-RW             2     1       9.4GB
 DVD+RW             1     1       4.7GB
 DVD+RW             2     1       9.4GB

 Rewritable High Definition (10K cycles)
 Blu-ray (BD RE)    1     1      25.0GB
 Blu-ray (BD RE)    1     2      50.0GB
 See Blu-ray.

Sides and Layers

DVDs come in any combination of single or double sided with single or double layers. This shows the laser beam contacting the recorded surface in all of the possibilities.

DVD Vs. CD-ROM

At minimum, the capacity of a DVD is seven times that of a CD-ROM because its tracks, pits and lands are more than twice as dense. It also uses more efficient recording algorithms. Add a second layer or record on both sides of the DVD, and capacity is doubled. (Image courtesy of C-Cube Microsystems.)