Reading a CD

The information is stored on a CD digitally, as a sequence of 1s and 0s. On the surface of a conventional CD this is represented by a continuous, microscopic track of bumps and flat areas that spirals out from the centre of the disc. An average disc is only 12 cm in diameter but the spiral of data can stretch up to 5 km in length!
Reading a 1 and 0 Images adapted from www.howstuffworks.com To read the CD a laser follows the spiral track. As the laser passes over a flat area the light bounces back into an optical sensor which reads a binary 1. When the laser reaches a bump the light is reflected away form the sensor and a binary 0 is registered.