News and Reviews....

Not all DVD's Are Created Equal.....    January 2002

Unlike VHS, where a movie's length determines the amount of tape needed, DVDs are made in a specific size. There are four variations in DVDs even though they look the same and their differences are transparent to the consumer, but they are very different in nature.

To begin, lets establish the fixed numbers of a DVD and its differences and similarities to the CD.  It has a 12cm diameter and 1.2mm thickness like a CD. It uses a RED laser diode in place of the Infrared laser of a CD drive. The  RED laser's shorter wavelength of 650nm as compared with the 78nm for the CD allows the "pits" to be condensed more densely in the tracks and the tracks to be squeezed more tightly together.

The initial DVD released was the DVD- 5 comprised of a two layer process but a Single Layer Format. The top layer or substrate is a dummy with no information, but added to reduce warping. The DVD-5 can thereby be classified as a single-sided, single -layer format holding 4.37 gigabytes of information.

To increase the time element and information that a disc can hold, the DVD industry developed the DVD-9 process. Whereby the DVD became a Dual-Layer Format utilizing the dummy top layer and expanding its storage capabilities to 7.95 gigabytes. It is a single-sided, dual-layer format. Now the top layer which is also accessed (read) from below requires the DVD Player to re-focus its laser reader to the upper second layer. To reduce cross talk, the minimum pit length of both layers is increased and the scanning velocity is slightly faster. The result are fewer pits per revolution, which results in slightly less capacity per layer. Many of the original DVD players where upgraded as the DVD-9 came into being due to a number of inherent problems associated with the change.

There are two more types of DVDs, the DVD-10 and DVD-18. The DVD-10 consists of two DVD-5s back to back which yield 8.74 gigabytes, and the DVD-18, consisting of two DVD-9s which yields 15.9 gigabytes. Both require the disc to be turned over to access the remaining information if used in contiguous form, or as generally used, to supplying one side in 4:3 format and the other in 16:9 Wide Screen.

The future may hold a DVD-14 which will be a DVD-5 and DVD-9 back to back. More so, the industry seems to be shifting toward DVD-9 as the mainstay to reduce the flipping over problem on longer feature titles and as more bonus information is added. No one likes to get up within a showing to flip the disc and the problem becomes more of a hassle as large DVD libraries are loaded into changers to make organization of discs easier. Changers don't necessarily have to be front and center, only accessible for loading of new discs.

More to come (I'm sure) on this fabulous technology ............