![]() ![]() The data are stored on the disc with a laser or stamping machine, and can be accessed when the data path is illuminated with a laser diode in an optical disc drive that spins the disc at speeds of about 200 to 4,000 RPM or more, depending on the drive type, disc format, and the distance of the read head from the center of the disc (outer tracks are read at a higher data speed due to higher linear velocities at the same angular velocities). The encoding pattern follows a continuous, spiral path covering the entire disc surface and extending from the innermost track to the outermost track. The encoding material sits atop a thicker substrate (usually polycarbonate) that makes up the bulk of the disc and forms a dust defocusing layer. Their main uses are the distribution of media and data, and long-term archival. ![]() DVD), or store both on the same disc (e.g. Optical discs can store analog information (e.g. ![]() Optical discs can be reflective, where the light source and detector are on the same side of the disc, or transmissive, where light shines through the disc to the be detected on the other side.
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