Disk format for storing digital information. Double-layer double-sided DVDs can hold 28 times the data stored on compact discs (CDs). Pre-recorded DVDs, first released in 1996, can hold a full-length feature film and many extras. As with CDs, information is etched in the form of microscopic pits onto a plastic disk (though the pits are half the size), which is then coated with aluminium. DVDs may have two pitted surfaces (layers) per side whereas CDs have only one. The data is read optically using a laser as the disk rotates. A double-layer disk can hold four hours of video per side.
The capacity of a DVD can be 4.7 gigabytes (single-sided, single-layer – the most common), 8.5–8.7 gigabytes (single-sided, double-layer), 9.4 gigabytes (double-sided, single-layer), and 17.08 GB (double-sided, double-layer – a rare format). The Blu-Ray format, released in 2006, was designed to supersede the DVD. It uses a blue laser for recording and playback rather than a red one. The shorter wavelength of the laser allows more data to be recorded, and Blu-Ray disks can hold up to 27 gigabytes (50 gigabytes on a double-layer disk).
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