Pulsing at high power, the laser in the drive can ablate or "burn" marks in the dye. In addition to a layer of metal, the media includes a thin layer of dye. The blank grooves can keep the drive on track before the data is written. To make a recordable disc, you start with a plastic substrate that has blank grooves rather than a predefined pattern of pits. The regular topography on the disc ( see atomic force microscope scan, top right) causes the reflected light to "modulate" from bright to dark as the laser beam scans from an area with no pit to one with a pit as the disc spins under the focused laser beam in the drive.
New technology made that possible a few years later with CD-R (recordable CDs) and then CD-RW (rewriteable CDs).ĬD-Audio and CD-ROM feature a spiral of pits on a molded plastic substrate overcoated with a reflective aluminum alloy. But soon the consumer, accustomed to recording LPs onto magnetic tapes, demanded the same ability in the new compact disc format. This digital format was very quickly accepted as the standard because it provided compact size, high fidelity and tremendous durability. CD-Audio and CD-ROM were established in the early 1980s as the "new thing" to replace the venerable analog long-playing record.
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