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The “pregrooved” disc is necessary in order to provide the recorder with a physical reference. The groove also contains timing information that the recorder uses to keep the CD spinning at the correct speed at all points along the disc surface. After the polycarbonate substrate is molded, the disc is spin-coated with the recording layer, an organic dye such as cyanine, phthalocyanine, or azo. The recording layer is then coated with a vacuum-deposited reflective layer, followed by a spin coat of