How is the information physically stored on the CD?
Answer A pre-recorded CD contains raised and lowered areas, called “lands” and “pits”. The laser in a CD recorder creates marks in the disc’s dye layer that have the same reflective properties. The pattern of pits and lands on the disc encodes the information and allows it to be retrieved on a CD player or computer CD drive. Discs are written from the inner portion to the outside. On a CD-R, you can actually see the tracks after writing, if you were curious. The spiral track makes 22,188 revolutions around the CD, with approximately 600 track revolutions per millimeter as you move toward the outer edge. If it were possible to “unwind” this spiral, it would be around 3.5 miles long.
