DVD Double Layer (DVD9) Technology:

A single layer DVD (DVD5) has one layer, which unlike a CD, is sandwiched in between a disc. A Double Layer (DVD9), however, has two layers; both of which (like a single layer DVD) is sandwiched in between a disc. In a DVD Double Layer (DL) disc, an ultra-thin spacer separates these two layers.

Since a single layer DVD can hold 4.7GB, it is called DVD5, because 4.7 rounded is five. And, a Double Layer DVD’s capacity is 8.5GB, also rounded, is nine.

Each layer has a metal reflector on top of it, to reflect the laser’s light, (this is how it is read). How DVD DL technology works is, the laser of a DVD DL burner/reader first focuses itself on the second (upper) layer of a disc. The lower layer's reflector in a DVD DL is different from a single layer's reflector, in that it is semitransparent.

 

DVD DL Edge Illustration

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What the laser of a DVD DL burner/reader is able to do, is focus itself past the lower layer’s semitransparent reflector onto the second (upper) layer. Allowing it to read and/or write to that layer. The advent of this technology nearly doubles a DVD’s capacity, from 4.7GB (Gigabytes), to 8.5GB.

And, of course, since the layer(s) of (a) DVD5/DVD9 disc(s) is/are not exposed, the disc is extremely durable.

 

Last updated: 07/01/04