Music CDs you buy in the store that have actual pits and grooves on a metal disc encased in clear plastic. The peaks and valleys cause the laser light to either be reflected back to the light sensor or directed away from it. When light is detected by the sensor, this is interpretted as a "1" or "on" bit of data. When no light is detected, this signals a "zero" or "off" bit. By combining a series of 1's and 0's together, you get the information that makes up the music data on a CD.

Recordable CDs also provide these 1's and 0's, but in a slightly different way. Instead of actual pits and grooves like the commercially produced CD, a dye layer is altered by a recorder to be either reflective or non-reflective. Reflective parts are 1's and non-reflective parts are 0's.

One issue with this method is the lifespan of the dye layer. Excessive light or temperature changes can degrade the dye layer and lead to data loss. Therefore, recordable CDs should not be relied on as your only storage medium.