What of the DVD Forum and the its dash format? While not available at the time of this writing, it's expected that the DVD forum will offer a recordable dual layer disc specification in the near future and probably within 2004.
DVD+R DL vs DVD-R DL
Double Layer Media (DVD+R DL) or Dual Layer Media (DVD-R DL), means that much like commercially pressed DVD-ROMs, these recordable discs have two layers of dye, almost doubling the size of older DVD5 format to 8.5gb. This is a recordable DVD9 format. Only dvd burners with Double Layer DL DVD R Media compatibility are able to burn the Double Layer Media. If your dvd burner does not have the capabilities, it is possible to be upgraded to burn Double Layer media. Check with your burner manufacturer for details. Other ways to say it is DVD+R DL media, Double Layer DL Media, Dual Layer Media, and DL DVD R Media.
The DL DVD+R (double-layer) media is the newest technology breakthrough in optical discs. The advanced, single-sided disc has an amazing 8.5GB of storage capacity, enough for up to four hours of DVD-quality video, 16 hours of VHS-quality video, or over 120 hours of MP3 audio. It is compatible with all current DVD video players and DVD-ROM drives as well as new DVD+R DL drives. The disc is ideal for virtually any business or household application.
This DVD DL technology allows material to be either read or recorded on one layer without affecting material on the other layer. An important advantage of the double-layer configuration is convenience. It allows users to read, write, or view nearly twice the amount of data than with the currently popular single-layer 4.7GB DVD discs without having to flip sides or change discs.
While consumers around the world have enjoyed burning their own DVDs for a few years now, the inevitable question of “what’s next” is now upon the industry. Certainly, blue laser technologies such as Blu-Ray will one day become affordable and prevalent; however, consumers today are still very much in love with DVDs. The DVD format is mature, high-quality content is widely available, and players are low cost and now installed in approximately 53 percent of U.S. households.
Dual layer DVD technology is not new. Commonly called “DVD9,” Hollywood has been churning out major motion pictures on stamped dual layer DVD Discs for years. How else could they include the full length movie plus all the bonus materials commonly found on today’s DVDs? Because dual layer technology has always been part of the DVD specifications, dual layer DVD recording on the desktop is the natural progression of single layer 4.7GB recordable technology.
Single-sided dual layer recordable discs are constructed by one dummy polycarbonate platter base and a single organic recording layer. Dual layer DVD-R 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. Single layer DVDs have a wobbled pre-groove molded into the polycarbonate base that controls the rotation speed of the disc and provides the addressing scheme for the disc. In a dual layer recordable DVD, 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 layer recordable disc is contained only on the first recordable layer (L0).
Burning Double Layer / Dual Layer DVD - How does it work?
When a dual layer recordable disc is inserted into a dual layer-compliant recorder, the optics will 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 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 disc to determine whether the disc is completely blank, partially recorded in Multi-session format, or Finalized (completed).
The two layers represent one contiguous address stream for recording as a Video Disc, a DVD-ROM, or even a packet recorded disc. When recording on dual layer 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 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 recordable media, so it’s possible to add data in “sessions” on a disc.
Reflectivity of both recording layers of a dual layer recordable disc is the similar: greater than 18 percent. The reflectivity between the L0 and L1 layers, however, is greater than 50 percent because the upper (second) recording layer 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 layer 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 by simply changing the position of the laser’s object lens.
Both the DVD Plus (“+”) and Dash (“-“) formats are still very much alive and well and appear to be with us for the foreseeable future. Presently, the DVD+RW Alliance is the first of the two organizations to present a Dual Layer recordable standard. The formal name of the format is Double Layer. Initially available only in a write once format called DVD+R DL, this technology should debut by the middle of 2004 with drives and media from several major manufacturers, including Sony. Recording speeds for DVD+R DL are initially 2.4X, however, they are expected to increase in the future. Drives supporting DVD+R DL will also be able to record single layer discs at up to 8X or faster (using write once media) and support high-speed CD-R/RW burning as well.