Dual DVD disc

	Dual DVD disc


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Dual DVD disc

Dual DVD disc, which is also called dual layer DVD, looks almost like a standard DVD, but gives you space from two to four times as much as the standard one.

Dual DVD recordable discs contain two organic dye recording layers (termed L0 and L1, respectively) between dual polycarbonate bases and semi-reflective metal layers separated by a transparent spacing layer. In a dual DVD made for recording purposes, each recording layer has its own wobbled pre-groove that controls rotation speed and addressing for that layer. However, the entire "table of contents" and system area of a dual DVD recordable disc is contained only on the first recordable layer (L0).

When a dual DVD recordable disc is is inserted into a dual layer-compliant recorder the optics will focus the laser at one of the dual DVD layers to try and detect an "Address In Pre-groove" (ADIP) signal. From the ADIP signal, the recorder can detect whether the dual DVD disc is dual layer and which layer it's focused on. Once the media type and the layer are detected, the laser will be able to move its range of focus down or up to access any one of the two recordable layers. The drive will then focus on the Lead-In area of the dual DVD disc to determine whether the disc is completely blank, partially recorded in Multi-session format, or Finalized (completed).

Dual DVD discs have the same reflectivity of both recording layers: greater than 18 percent. The reflectivity between the L0 and L1 layers, however, is greater than 50 percent because the upper (second) recording layer of dual DVD absorbs and reflects some of energy that is directed at the lower (first) recording layer L0 in order for organic dye to be recorded. As a result, the organic dye formulation and shape of the pre-groove in dual DVD discs must be optimized to provide the appropriate reflectivity for both layers. The spacer layer separates the two recording layers and prevents cross layer recording. It is transparent to allow the laser to easily focus on either recording layer of dual DVD by simply changing the position of the laser's object lens.


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