|
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. |
