A spiral of tiny changes in reflection
A CD stores information along one continuous spiral track, beginning near the center and winding outward. The track is molded into the clear plastic as microscopic pits and flat areas called lands. These features are not read as a simple pattern of “pit equals one, land equals zero.” Instead, transitions between them change the reflected laser light in a way the player can detect and decode as digital data.
The disc’s aluminum coating supplies the reflective surface. As the laser scans the spiral from the underside, a sensor measures the returning light. The player turns those tiny changes into a stream of bits, then uses error-correction data built into the recording to recover information when small defects interfere.
Why the label side can be more vulnerable
The clear plastic on the underside is relatively thick, so a shallow scratch there may scatter the laser without reaching the recorded features. The player’s error correction can often compensate for a limited amount of that interference. A deep scratch on the label side is more serious: the reflective coating and data-bearing layer lie close beneath the label, so damage can remove or disrupt the track itself.
That difference explains a practical handling rule: avoid scraping either surface, but take particular care not to gouge the label side. A mark that looks small from above can cut across the spiral and erase a section of the signal the player needs to reconstruct the recording.
