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轉載自 http://www.cdfreaks.com/article/129

The dual layer DVD recordable - Article

Posted by Jan Willem on 26 November 2003


A dual layer DVD is a DVD that contains two layers of data. Pressed dual layer DVDs (like movie DVDs – DVD-ROM - you purchase in a store) have been on the market for quite some time now, but recordable dual layer DVDs are not available yet. Current DVD recordables can contain up to 4.7 Gigabytes of data, a dual layer DVD recordable could contain up to 8.5 Gigabytes.

Recently Philips Research announced the feasibility of dual layer DVD technology and their announcement was quickly followed by an announcement of competitor Pioneer in which they announced that they were also planning to bring dual layer DVD technology on the market. Although the technology might be (partly) ready, it will take some time before it will be widely available on the consumer market.



The announcements raised many questions by our visitors. For more information on the dual layer DVD recordable formats we contacted both Philips and Pioneer

Background



In order to be able to understand the story you first might like to know that currently there is a DVD recordable format race going on. In the CD recordable days you could just purchase a CD-R and burn it, in the DVD recordable era this has changed. Currently there are three recordable DVD formats, DVD-RAM, DVD-RW and DVD+RW. DVD-RW is mainly developed and promoted by Pioneer while DVD+RW is mainly developed and promoted by Philips. If you want to burn a DVD+R disc you will need a DVD recorder that is able to write this format and for DVD-RAM and DVD-RW the same applies. Some companies though, offer drives that support multiple formats.



The dual layer format has once again shown that the format fight is not over. DVD-RAM is no longer seen as a real competitor on the PC DVD recorder market and the battle is mainly between DVD-RW and DVD+RW. Knowing this, it’s not strange that both companies/formats have announced the dual layer recordable DVD right after each other.



The Technology



Simplified, a DVD recordable contains a layer of a chemical substrate that is hit (burned) by a laser. The laser creates small holes in this chemical substrate. This way it creates so called pits and lands, for normal PC users better known as 1’s and 0’s. A dual layer contains two layers of this chemical and by adapting the laser intensity both layers can be written. Of course this is a very complicated process and requires a lot of precision and the right materials to make sure that after the data has been burned, it can still be read back without errors.



Reading back has been the biggest challenge in development of the format, as current DVD players were not designed to read back dual layer DVD recordable discs. However they are able to read back pressed (DVD-ROM) dual layer discs, so the developers have been focusing on making the DVD recordable compatible with the DVD-ROM dual layer discs.



The (near) future


We asked both Pioneer and Philips for more information regarding this matter. For completeness of this article we should add that only Philips has really demonstrated the technology. Until now nobody has seen anything from Pioneer outside their Research and Development labs. As where Philips says they will release products in the first half of 2004 and already has announced real life products, Pioneer has only announced they’re working on the technology, but told us that they hope to ship products within the year 2004. Also the introduction speed of Pioneer is unknown; Philips could be more specific and told us that the first generation of dual layer writers will write the discs at 2.4x.

Philips has another advantage as it jointly developed the technology with Mitsubishi Kagaku Media (better known by its Verbatim brand). Pioneer has no media partner but Mr Yoshimura from Pioneer Business Planning told us: “Our next step is to propose this technology to the DVD-forum. During technical discussions at the DVD-Forum all technical information will be provided to attendees. So once passed, major media manufacturers will be able to produce dual DVD-R discs easily”. This is also the road Philips is going to take, but it will make its technology available to the DVD+RW alliance members. The company expects to finalize the specifications in December 2003; Pioneer could not disclose any date.