A dual layered disc is holds more data. (almost) All the commercial DVD movies you buy from Walmart are dual layer disc.
Take for example DVD quality sound and video. For most DVD movies, 20 minutes of movie time takes up roughly 1 GB of data. So for a 2 hour movie we are using about 6 GB of data.
Now, you you look at most common DVD recorders (DVD-RW/+RW), you notice they only can record 4.7 GB of data. How do movie houses get 6GB of data if you can only record 4.7?
Well, the answer is because they use two layers.
Today, CD's and DVD Recordable media are single layer. They look (over simplified) something like this.
--------- <--Top Label
******* <--Reflective Layer (contains the bumps that hold the data)
--------- <--polycarbonate
That single reflecive layer is what the laser in the drive focuses on and holds that 4.7 GB of data.
In a dual layer format, it addes a layer and looks somewhat like this:
--------- <--Top Label
******* <--Reflective Layer (contains the bumps that hold the data)
--------- <-- Polycarbonte
******* <--semi-transparant Reflective Layer
--------- <--polycarbonate
They add a semt-transparent (translucent, whatever!) layer and basically double the capacity of the disk (it's actually less than double since the translucent layer can't hold quite as much data - I think the dual layer discs can hold 8.5 GB of data). The laser in the drive needs to know how to focus on two spots. Thus you need a drive that supports the dual layer format. Obviously you will also need to buy blank dual layer DVD media to use both layers. You are still supposed to be able to use the single layer media of today on the dual layer drives of tomorrow but will only get 4.7 GB on them.
Last I heard, some dual layer drives are supposed to ship this spring or summer. Should you wait till then or buy one now? Depends. You can also wait for BluRay format drives.. (i'm too tired to explain BluRay - go look it up on google). But by the time BluRay is about to come out, the next thing will be talked about.. It's like way back when i was like.. should I buy that 486dx2 now or wait for the Pentiums to come out. Then I considered going to the P90? naw, the 100's are coming out soon.. then the 100's came out and I was like, naw, I'll wait for the P133. Then the 133's came out and I was like, hmm.. PPro200's.... *drool*, then when those came out, I was waiting for the pentium II's. Then when those came out, I was waiting for the AMD K6's.. then it was the P3's.. and the Athelons.. until finally i looked at myself still running my 386sx20 measuring my speed in Mhz while the world around me had advanced past 1 GHz and thought.. man, I'm a sad.. sad.. fool.
Ugh, it's late and i'm rambling.. gotta go to bed.
