Why Dual layer DVD have 8.5GB capacity ?

[maroon1]

As I know the DVD have 4.7GB capacity for each layer.
Then if each layer has 4.7GB then dual layer must have 9.4GB, right ?

But why most dual layer DVD says that it has only 8.5GB capacity ? why not 9.4GB?

 

[KSoD]

It is Dual layer yes but it doesn mean that it just doubles the single layer disc.

A Dual Layer can not use the full capacity for the 2nd layer since it is smaller than the original layer.

------------------- < Top Plastic
~~~~~~~~~ < 2nd Burning Layer
------------------- < Middle Plastic
```````````` < Bottom Burning Layer
------------------- < Bottom Plastic

That is how it looks from a side view for a DL DVD. Now with all those layers put together in a DVD format the 2nd layer gets compressed to much and the laser cant use the full space like it can for the first layer. So that is why a DL DVD can only be 8.5GB instead of 9.4GB. I hope this helps.

 

[talldude123]

I've got a question about dual-layer, now that people are talking about it.

My new computer has a dual-layer DVD writer. Does this mean that if I buy the discs, it will write them as dual-layer, and be able to save more space? I don't understand what dual-layer means, or is.

 

[KSoD]

Dual Layer is a specific type of disc. There are single layer discs and dual layer. The dual layer are more expensive still.

Plus DL still burns slower than single layer. It is only at like 6x right now instead of 16x like single layer.

To show you a comparison here is a 100 Pack of DVD+R that goes for about $37.
http://www.newegg.com/Product/Product.asp?Item=N82E16817501004

Now 25 pack DL DVD+R that goes for $35.
http://www.newegg.com/Product/Product.asp?Item=N82E16817501007

DL is still quite a bit more expensive. This is what movie release DVD's are is DVD9 (Dual Layer) to help try and prevent copying since they are larger than regular DVD's.

 

[talldude123]

I think this new burner burns DL at 4X, which is pretty slow, with regular DVD's burning at 8X.

I'd only need DL DVD's for one reason, and that reason is *keep mouth shut*.

 

[KSoD]

Believe it or not. You dont need it for that. Google DVD Shrink. Version 3.2, it is a free app.