The CD, better known by its acronym CD, are devices used to store information. There are different types of CD. One of the most popular is the CD-ROM (Compact Disc-Read Only Memory) is read-only, ie you can not add or modify information in it. Other rules are the Photo CD, which you can view images, the CD-DA, through which sounds are played, the CD-R, which can record data, and the CD-I (Compact Disc-Interactive ), an optical disc that combines audio with the video and text. The CD-I allows the display of images in addition to the processing of special effects, animations and sounds.
The information contained on a CD is recorded in a spiral track that describes more than 20,000 cycles around the disk.
On its surface, which is coated with a layer of material that reflects light, are made microscopic holes that let the light beams, and are alternated with another area that reflects it. The first corresponds to a binary zero, and the latter by one. A laser beam that travels through the CD reads the stored information.