DVD, also known as Digital Versatile Disc or Digital Video Disc, is an optical disc storage media format, and was founded in 1995. Its main uses are video and data storage. DVDs are of the same dimensions as compact discs (CDs), but store more than six times as much data.
Variations of the term DVD often describe the way data is stored on the discs: DVD-ROM (read only memory) has data that can only be read and not written; DVD-R and DVD+R (recordable) can record data only once, and then function as a DVD-ROM; DVD-RW (re-writable), DVD+RW, and DVD-RAM (random access memory) can all record and erase data multiple times. The wavelength used by standard DVD lasers is 650 nm; thus, the light has a red color.
DVD-Video and DVD-Audio discs refer to properly formatted and structured video and audio content, respectively. Other types of DVDs, including those with video content, may be referred to as DVD Data discs.
The major disc on the current market can be seperated into two type: DVD-5 & DVD-9. DVD-5 is a single-sided and single-layered disc. DVD-5 indeed held five gigabytes, but some parameters were changed later on as explained above, so the capacity decreased. DVD-9 is a single-sided and double-layered disc. Its capacity is twice as much as DVD-5. At present, this two kinds of DVD is the mainstream on the market.
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