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From dusk to disc


Compact discs (CDs) and digital video discs (DVDs) store information in the same way. The disc's surface is marked with indentations arranged in a continuous spiral. As a laser moves across the pits, its beam is reflected back to the player, which reads the reflections as a signal and turns it into audio, video, graphics, or text. DVDs store more data than CDs because the pits are smaller and arranged in tighter circles. To transmit and process the added information, the DVD system requires more efficient compression and decompression technology.

For even more capacity, DVDs can have a second layer of pits laid over the first. The first layer is semireflective, allowing the laser to alternately read the data on the first layer or pass through and read the second layer. This added layer almost doubles the disc's capacity from 4.7GB to 8.5GB.

Although the first DVD releases will have data on one side, future discs could be double-sided, boosting the capacity to as much as 17GB. Despite DVD's greater capacity and enhanced compression, DVD drives and players will be able to read audio CDs as well as multimedia CD-ROMs.