Compact Disc

A Compact Disc (CD) is a disk which stores information on it. One side is blank for titles and the other side has the information on it. The middle is a hole for the disk drive to hold it.

Workings
The CD itself has thousands of miniscule pits on it, in a spiral going from the middle to the outside. A CD drive reads these pits using a laser, which reflects off these pits. When the laser hits a pit, the laser is reflected onto a light detector. When the laser hits a land (space between the the pits), the laser reflection misses the light detector. A tracking system moves the laser from the middle of the disk to the outside and as the laser moves outwards, the disk spins slower to account for the larger spirals.

Uses
A CD is used for storing many things, including games, music and information storage. It is usually used for applications which are sold in shops, such as Microsoft Office, or games.