CD Burning Technology
CD Basics: The Bumps
CDs store music and other files in digital form –that is, the information on the disc is represented by a series of 1s and 0s. In conventional CDs, these 1s and 0s are represented by millions of tiny bumps and flat areas on the disc's reflective surface. The bumps and flats are arranged in a continuous track that measures about 0.5 microns (millionths of a meter) across and 3.5 miles (5 km) long.
A CD has a long, spiraled data track. If you were to unwind this track, it would extend out 3.5 miles (5 km).
To read this information, the CD drive passes a laser beam over the track. When the laser passes over a flat area in the track, the beam is reflected directly to an optical sensor on the laser assembly. The CD drive interprets this as a 1. When the beam passes over a bump, the light is bounced away from the optical sensor. The CD drive recognizes this as a 0.
CD Basics: The Path
The bumps are arranged in a spiral path, starting at the center of the disc. The CD drive spins the disc while the laser assembly moves outward from the center of the CD. At a steady speed, the bumps move past any point at the outer edge of the CD more rapidly than they move past any point nearer the CD's center. In order to keep the bumps moving past the laser at a constant rate, the drive must slow the spinning speed of the disc as the laser assembly moves outward.
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