DVDs - "How they Work"

A DVD is the same diameter and thickness as a CD, and is made using some of the same materials and manufacturing methods. Like a CD, the data on a DVD is encoded in the form of small pits and bumps in the track of the disc. Typically DVDs are produced using DVD replication or DVD duplication for smaller runs.

A DVD consists of several layers of plastic approximately 1.2 millimeters thick. Each layer is created by injection molding polycarbonate plastic. The DVD disc has microscopic bumps arranged in a continuous, long spiral track of data.

Once the clear pieces of polycarbonate are formed, a thin reflective layer is sputtered onto the disc, covering the bumps. Aluminum is used behind the inner layers, but a semi-reflective gold layer is used for the outer layers, allowing the laser to focus through the outer and onto the inner layers. Once all the layers are created, each one is coated with lacquer, squeezed together and cured under infrared light. For single-sided discs, the artwork is printed onto the non-readable side. Double-sided discs are printed only on the non-readable area near the hole in the middle.

Each writable layer of a DVD has a spiral track of data. On single-layer DVDs, the track always circles from the inside of the disc to the outside. Because the spiral track starts at the centre, a single-layer DVD can be smaller than 12 centimeters if desired.

You will often read about "pits" on a DVD instead of bumps. They appear as pits on the aluminum side, but on the side that the laser reads from, they are bumps.

The microscopic dimensions of the bumps make the spiral track on a DVD extremely long. If you could lift the data track off a single layer of a DVD, and stretch it out into a straight line, it would be almost 7.5 miles long! That means that a double-sided, double-layer DVD would have 30 miles (48 km) of data!

To read bumps this small you need an incredibly precise disc-reading mechanism.

If you would like to talk to us about DVD replication or DVD duplication then please feel free to contact us, we will be pleased to answer any questions which you may have.