CDs very useful

CDs or compact discs are optical discs used to store digital data. During their manufacture, this disc is etched with microscopic bumps, arranged as a single, continuous, extremely long spiral track. The bumps store the data in a coded form.

   

             The surface of a CD is reflective because the disc is coated with a thin layer of aluminum. The shiny metal layer reflects the laser that is used to read or write the device. A layer of lacquer is then spin-coated onto the CD to protect the metal.

              Since nothing touches the encoded portion, the CD is not worn out during use, which makes them very useful for storing information.