These images show the marks on a compact disc. The technology behind the compact disc uses lasers to burn lines and dots to record data. Rather than encoding the ones and zeros directly, the reader relies on the change of the status from a landing to a pit. The pits are the locations where the laser has burned the CD. Burning the CD alters the reflectiveness of the polymeric material used. When a change happens from a pit to a landing or vice versa, a 0 is read. If no change happens, it is encoded as a 1. This change-based encoding minimizes the on/off cycles of the laser, improving its life span. Using binary encoding, practically any data can be recorded and read by lasers. The starting point of the data recording on this particular disc is visible in some of the images. The bottom section of the image has no data recorded. Therefore, no lines or dots are seen in this section. Due to the high magnification of the images (approximately 1800X on your computer screen), the circular sections appear more like lines, hiding the actual curvature.
A comparison of a Compact Disc and a DVD would be interesting to see. It is supposed to have a denser data recording.