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DVD Capacities:

DVD discs have the same physical dimensions as CDs, but each DVD comprises two substrates each 0.6mm thick and bonded together much like a sandwich.

This allows for the possibility of discs with up to two sides and up to two layers offering four possible read-only formats plus recordable and rewritable formats:

DVD-5 4.7GB 1 1 Read from one side only
DVD-9 8.54GB 2 1 Read from one side only
DVD-10 9.4GB 1 2 Read from both sides
DVD-18 17.08GB 2 2 4 layers, read from both sides
DVD-R 4.7/9.4GB 1 1 or 2 Recordable DVD
DVD-RAM 2.6/5.2GB 1 1 or 2 Rewritable DVD
DVD-RW 4.7GB 1 1 or 2 Re-Recordable DVD

DVD Disc Layout
Each layer of a DVD disc contains lead-in, data area and lead-out like a CD. For dual layer (DVD-9) discs the two layers comprise a single volume, but can be organised in two different ways depending on the application:

Parallel Track Path PTP), where the two layers both start at the inside diameter (ID) and end at the OD with the lead-out. This is suitable for DVD-ROM.

Opposite Track Path (OTP), where layer 0 starts at the ID and layer 1 starts where layer 0 ends. For such discs there is one lead-in (on layer 0), one lead-out (on layer 1) and two middle areas. This is suitable for DVD-Video where a single movie can occupy both layers with a layer break in the middle. Using OTP allows a near seamless jump from layer 0 to layer 1.

DVD-5 (4.7GB) Single Sided/Single Layer
This is the simplest of the family of DVD discs, comprising a single layer with a capacity of 4.7GB. Only one of the two 0.6mm substrates contains data, the other being a blank disc. The two substrates are bonded together to form a 1.2mm thick disc.

Single sided discs can be printed on by any conventional method eg screen printing. Alternatively, the blank substrate can be moulded with an image in its surface and then metalised to make it visible.

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-10 (9.4GB) Double Sided/Single Layer
This disc comprises two sides each single layer. It differs from the DVD-5 version in that both substrates contain data. To read both sides the disc will need to be turned over for most DVD players/readers. The capacity is 9.4GB, twice the single side/single layer version.

Double sided discs cannot be printed except on the hub inside the lead-in area. Labelling is therefore a problem with such discs.

DVD-18 (17.1GB) Double Sided/Dual Layer
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.

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