Layers of a DVD

DVDs are the same size and shape as conventional CD’s and have the same inner hub diameter. However, unlike CD’s they are capable of storing up to 5 times more data.

Like a CD’ data is stored on a DVD in binary format, represented by a pattern of pits and bumps on the surface of the DVD. These pits and bumps are again interpreted by the DVD player as audio and video.

A DVD is constructed by squeezing together up to 4 layers of polycarbonate plastic, each only 0.6mm thick. Each layer contains a tightly spaced spiralling track. The construction process results in a disc that has one continuous (and very long) track of ‘bumps’. These bumps spiral towards the outer of the DVD and represent the data stored on the DVD. Just 740 nanometres divide each track from the next.

Each bump on the DVD surface is approximately 320 nanometres wide, at least 400 nanometres in length and 120 nanometres high. Incredibly, the track on a full, single layer DVD, would cover a distance of 7.5 miles if it were laid out straight. A double layer DVD can hold the equivalent of 30 miles worth of data!

Once the layers of polycarbonate are complete, a thin layer of reflective material is spun onto the surface of the disc to cover the bumps. Aluminium is used to coat the inner layers, while slightly reflective gold is used to coat the outer layers. The gold coating is designed to help the reading laser focus on the inner layers.

Each of the various layers are coated with a resin and squashed together to form the finished DVD. The non-readabl3 side of the DVD is often printed upon using a silkscreen printing process, or labelled using a sticky label.