Dual layer DVD media

	Dual layer DVD media


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Dual layer DVD media

Dual layer DVD media is a little bit more complex than it is for the standard DVD or CD.

Dual layer DVD media contains 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 dual layer DVD media 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 dual layer DVD media is contained only on the first recordable layer (L0).

Dual layer DVD media enables optics in a dual layer-compliant recorder to focus the laser at one of the dual layers to try and detect an "Address In Pre-groove" (ADIP) signal. From the ADIP signal, the recorder can detect whether the dual layer DVD media is dual layer and which layer it's focused on. Once the dual layer DVD 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 of the dual layer DVD media. The drive will then focus on the Lead-In area of the dual layer DVD media to determine whether the disc is completely blank, partially recorded in Multi-session format, or Finalized (completed).

Dual layer DVD media represents one contiguous address stream for recording as a Video Disc, a DVD-ROM, or even a packet recorded disc. When recording in dual layer DVD media, the drive first records on the first recordable layer L0 from the inside hub area outward, just like a typical DVD recordable disc. When the end of information recorded in L0 is reached, Middle Zone 0 is added. Next, the drive focuses on the second recordable layer L1 of dual layer DVD media to create Middle Zone 1 that over-wraps Middle Zone 0. The disc is then recorded from the outside rim inwards. Multi-session discs can be recorded with dual layer DVD media, so dual layer DVD media supports multiple "sessions" on a disc.


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