DVD originally stood for Digital Video Disc but it is now more often called Digital Versatile Disc because it can be used to store computer data as well as video and audio data.  DVD is a format based on the compact disc.  It is 5 inches in diameter and can store over 8 hours of video. The data on a DVD is compressed using MPEG-2 digital compression.  This compression technology minimises the need to store repetitive data.  There can be two layers on each side, which means by slightly changing the focus of the laser that is reading the disc, a layer below the surface layer can be accessed.  This increases the storage capacity, especially when DVDs can be double sided as well.  Approximately 2 hours 13 minutes of video can be stored on a single-sided single-layer disc as well as 8 soundtracks.  A dual-layer disc provides 4 hours of video data and does not need to be turned over.     With the introduction of the Digital Versatile Disc, or DVD, in 1997, excellent quality pictures and sound are available to the home viewer.   DVD gives a better quality picture than laserdisc and especially VHS tape.   A DVD player will play movies, CD and Video CD.  Added to this, DVD has the option of multiple camera angles, different ratings, subtitles, karaoke, aspect ratios, which are all selected by an on-screen menu.