digital versatile disc
digital versatile disc or digital video disc (DVD), a small plastic disc used for the storage of digital data. The successor media to the compact disc (CD), a DVD can have more than 100 times the storage capacity of a CD. When compared to CD technology, DVD also allows for better graphics and greater resolution. In the case of an audio recording, where the data to be stored is in analog rather than digital form, the sound signal is sampled at a rate of 48,000 or 96,000 times a second, then each sample is measured and digitally encoded on the 43/4-in. (12-cm) disc as a series of microscopic pits on an otherwise polished surface. The disc is covered with a protective, transparent coating so that it can be read by a laser beam. As with other optical disks nothing touches the encoded portion, and the DVD is not worn out by the playing process. Because DVD players are backward compatible to existing technologies, they can play CD and CD-ROM discs; however, CD players cannot play DVD and DVD-ROM discs.
DVD formats include DVD-Video (often simply called DVD), DVD-ROM, and DVD-Audio. DVD-Video discs hold digitized movies or video programs and are played using a DVD player hooked up to a standard television receiver. In a sense, DVD-Video players are the successors to the videocasette recorders (VCRs) that play VHS tapes. DVD-ROM [Read Only Memory] discs hold computer data and are read by a DVD-ROM drive hooked up to a computer. These disks can only be read—the disks are impressed with data at the factory but once written cannot be erased and rewritten with new data. DVD-ROM also includes recordable variations. DVD-R and DVD+R[Recordable] discs can be written to sequentially but only once. DVD-RAM [Random Access Memory], DVD-RW, and DVD+RW [ReWritable] discs can be written to thousands of times; they differ in their technical standards and, as a result, in the amount of information they can hold. Dual layer disks, such as DVD-R DL, record data on two different layers within the disk. Many DVD recorders can record in several different recordable DVD formats. Some recorders include computer hard drives that allow the user to record tens to hundreds of hours of material temporarily; the user can then select the material that will be transferred to a DVD. When DVD was released in 1996 there was no DVD-Audio format, although the audio capabilities of DVD-Video far surpassed those available from a CD; the DVD-Audio format was introduced in 1999.