How DVDs Work

Laser disc is an older technology. It offered a better picture and better sound than videotapes, and it is comparable to DVD. But the laser disc format is analog; DVDs are digital (see How Analog and Digital Recording Works). Laser discs are only used for prerecorded movies, and they are larger, about 12 inches (30.5 centimeters) in diameter, instead the 5-inch (12.7-centimeter) diameter of DVDs. The two formats usually can't be played on the same machine.

Laser discs, like DVDs, allow viewers to go to the exact scene they wish to see, and to freeze a frame or slow the picture. Laser discs can only hold an hour on each side, so you have to flip the disc to watch the second half of the movie.

Because of DVD compression techniques, DVDs can hold more data. You rarely have to flip a DVD to watch a whole movie. Laser disc players are noisier than DVD players, and they can sometimes suffer "laser rot" -- the aluminum side of the disc oxidizes, and the quality of the disc deteriorates. DVDs are less likely to have this problem, because manufacturing techniques have improved. As the popularity of DVD grows, laser discs are becoming harder to find.