Old vinyl LPs of yesteryear used a simple needle to travel along the grooves and reproduce prerecorded sound. Today, that needle has been replaced by a laser beam for both CDs and DVDs. The laser in a DVD player, for example, emerges from a tiny point and focuses on the different layers of the disc. As the lens move sideways, it reaches areas farther in or out on the disc. As lens moves along the beam, that is, longitudinally, it reaches different depths on the disc. All the information is stored in several layers as ones and zeros, and only one layer can be read at a time. Every point on a particular layer is read during every revolution of the disc. In order to make room for a lot of information on every disc, the beam has to be focused on as small an area as possible. This cannot be done with any other light source than a laser. Today this area has been reduced to about half a square micrometer, which yields 2 megabits or 0,25 MB(yte) per mm2.