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DVD-9 and DVD-18 discs Dual layer, single and double sided discs which are more difficult to make. |
DVD-9 (8.5GB) Single Sided/Dual Layer
This dual-layer, single sided version has a capacity of 8.5GB which is slightly less than twice the single layer version, to make it easier for the second layer to be read. Pits on both layers are 10 per cent longer than on a DVD-5 or DVD-10 disc.
Each layer is moulded in one substrate, the two substrates being joined with an optically transparent bonding layer. These discs can be printed after bonding in the conventional way.
DVD-18 (17.1GB) Double Sided/2 Layers
This version comprises two sides each with a dual layer format. Both layers of each side must be manufactured on a single polycarbonate substrate.
It has the largest capacity of the family but is the most difficult and complex to manufacture. Four stampers are needed to create the four layers.