Com 226 comp trouble shooting II theory book
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| Understanding CD Media CDs are mass-produced by stamping the pattern of pits and lands onto a molded polycarbonate disc (known as a substrate). This stamping process (much like the stamping used to produce vinyl records) places the data on the disc. But the disc is not yet readable— several finish steps must be performed to transform a clear plastic disc into viable, data- carrying media. The clear polycarbonate disc is given a silvered (reflective) coating so that it will reflect laser light. Silvering coats all parts of the disc side (pits and lands) equally. After silvering, the disc is coated with a tough, scratch-resistant lacquer that seals the disc from the element especially oxygen, which will oxidize and ruin the reflective coating. Finally, a label can be silk-screened onto the finished disc before it is tested and packaged. Figure 7-2 illustrates each of these layers in a cross-sectional diagram. Recordable media appears very similar to pressed CD media (Fig. 7-2), but with two important variations. First, the polycarbonate CD-R substrate is preformed with a track spiral into which data will be written during recording. The substrate is then coated with a greenish translucent layer, and backed with a reflective layer of gold before protective lacquer is applied over the gold. These translucent and gold layers allow the recorded pits and lands to be read back after recording. CARING FOR COMPACT DISCS A compact disc is a remarkably reliable long-term storage media (conservative expectations place the life estimates of a current CD at about 100 years. However, the longevity of a CD is affected by its storage and handling—a faulty CD can cause file and data errors that you might otherwise interpret as a defect in the drive itself. Here are some tips to help protect and maintain the disc itself Don’t bend the disc Polycarbonate is a forgiving material, but you risk cracking or snapping (and thus ruining) the disc. - Don’t heat the disk Remember, the disc is plastic. Leaving it by a heater or on the dashboard of your car might cause it to melt. - Don’t scratch the disc Laser wavelengths have a tendency to look past minor scratches, but a major scratch can cause problems. Be especially careful of circular scratches (one that follows the spiral track. A circular scratch can easily wipe out entire segments of data, which would be unrecoverable. - Don’t use chemicals on the disc Chemicals containing solvents, such as ammonia, benzene, acetone, carbon tetrachloride, or chlorinated cleaners, can easily damage the disc’s plastic surface. Download 1.89 Mb. Share with your friends:
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