Digital Versatile Disc (DVD), or DVD-Video as it is known, is an optical recording medium capable of recording videos over an extended period.

Its media composition, geometry and data recording and reading methods are basically the same as those of a CD, but through increased recording density, it offers a higher storage capacity of 4.7GB on single-sided single-layer recording type discs, 8.5GB on single-sided dual-layer type discs and 9.4GB on double-sided single-layer type discs. As a matter of course, DVD drives can also read CDs. A DVD-Video can store video data compressed in MPEG2 format and mainly 5.1-channel Dolby AC-3 digital audio data. But apart from this, it also offers functions such as encryption of recorded contents, control over branching and prohibited operations via a menu screen, multi-story, multi-angle, multilingual audio and subtitles, region codes (to restrict the distribution area) and parental control. Using its random access feature, the user can also shuffle play a DVD to view chapters randomly. Inclusion of encryption, region code and parental control functions is left to the discretion of the content creator and cannot be altered by the user. In particular, the region code is included in all elements associated with the reading of the recording medium to the reproduction of its contents. With a PC, for example, the contents cannot be played unless all of the region code settings match on the DVD-Video, drive mechanism, DVD playback software and, in some case, the operating system as well. That is why the dialogue, “Please select the region”, appears on a newly-purchased PC when playing a DVD-Video for the first time. This must be selected carefully because once the DVD drive’s region is set, it can only be changed 5 more times (or just one more time, depending on the model of the drive). Reinstalling the operating system will not reset this number of allowances.

Besides DVD-Video for video recordings, there are DVDs for other applications and purposes such as DVD-Audio for audio recordings and DVD-ROM for storing programs and data. Moreover, there is a wide variety of products in addition to the read-only DVDs above. They include the write-once DVD-R and the rewritable DVD-RW, DVD+RW and DVD-RAM. Please refer to the relevant sections for more information. The designation “XX-speed” on DVDs is based on the assumption that the speed for playing a single-sided single-layer disc in an hour is single speed.