Hi Jasen! :-)

 JB> DVDs have two data layers and select whuch one to read by focusing 
 JB> the laser on it.
Writable DVDs only have one layer. For prewritten stuff you can buy, both
layers are pressed seperately and then put together, something a DVD writer
in a PC cannot do. ;) This is also the reason that writable DVDs only have
half the capacity of pressed dual-layer DVDs.

Ciao
Pascal

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