They store 2x the data of a regular disc (4.7GB vs. 8.5GB) Also they cost 5x as much. You need a burner made in the last few years to burn those discs.
Double Layer Recording – The Basics Double Layer DVD technology is not new. Commonly called “DVD9,” Hollywood has been churning out major motion pictures on stamped Double 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 Double Layer technology has always been part of the DVD specifications, Double Layer DVD Recording on the desktop is the natural progression of single layer 4.7GB recordable technology. Double Layer DVD recordable discs offer up to four hours of high quality MPEG-2 video, or up to 8.5GB of data on a single sided disc with two individual recordable “layers”. Double Layer capable recorders will have the ability to record on the new Double Layer DVD recordable discs as well as traditional single layer DVD discs and CDs too. Want more? Because a recorded Double Layer DVD disc is compliant to the DVD9 specification, the discs are compatible with most consumer DVD players and computer DVD-ROM drives already installed in the market. The Recordable DVD Format Debate and Double Layer 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 Double 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. What of the DVD Forum and the Dash format? While not available at the time of this writing, its expected that the DVD forum will offer up a recordable Double Layer disc specification in the near future and probably within 2004. Certainly dual format DVD burners are overtaking the commercial market and Sony was the Pioneer of Dual Format burners. Sony is a member of, and is committed to continuing to support the DVD+RW Alliance and the DVD Forum for Double Layer DVD recordable/rewritable technology. Consumer Applications With up to four hours of high quality MPEG-2 video on a single sided disc, consumers can really take their home movies to the next level with Double Layer DVD recording. One benefit of the additional space is the ability to increase the bit rate of the video when authoring to get higher quality on the finished disc. Typical DVD authoring software applications use variable bit rate encoding to maximize utilization of the DVD disc space. By forcing the application to always encode at the highest bit rate supported, more space will be used on the disc, however the quality difference is noticeable and worth it. Double Layer DVD recording makes it possible for a consumer to create longer home movies and even consolidated many home movie projects onto a single disc. Let’s not forget that up to 8.5GB of uncompressed DVD disc space is a great place to store data and keep your PC’s valuable data, applications, and settings backed up for when disaster strikes. You can pack up to 12 CDs or 5,902 floppy disks’ worth of information onto a single Double Layer DVD disc. With the additional capacity of a Double Layer DVD recordable disc, a consumer can store approximately 2,000 songs in MP3 format or up to 17,000 high quality JPEG images. Talk about a cool place to store all that stuff cluttering up your hard drive! cheers
