This is coated with a thin layer of gold - enough to make it reflective but thin enough that the laser can penetrate through to the deeper layer. When the first layer has played, the laser increases its power output and its focal length, and reads the deeper layer. The data tracks are laid in opposite directions so the laser does not have to return to the centre of the disc to switch tracks. The amount of data on a double layered DVD is not quite twice as much as a single track DVD since the bumps have to be longer on both layers to avoid interference that would cause errors in reading the data. DVD look set to be with us for a while at least.
Recent models are now capable of reading our old CDs as well as DVDs.
I'm sure that in the near future we will be using this one system for all of our home entertainment - music, movies and computer games. To watch the flash movie you will need a Macromedia Flash plug-in available free by clicking here.