1146 Chapter 30
30.6.1 DVD Disc Manufacturing
A DVD thickness of 1.2 mm comprises two 0.6 mm
substrates, bonded together with the data layers placed
near the internal interface for greater protection. Thin-
ner substrates are optically more resistant to tracking
errors that result when a disc is slightly tilted relative to
the laser pickup. The dual substrate construction allows
manufacturing variants, yielding five types of play-
back-only discs: DVD-5 (single side, single layer),
DVD-9 (single side, dual layer), DVD-10 (dual side,
single layer), DVD-14 (dual side, mixed layers with sin-
gle layer on one side and dual layer on the other side),
and DVD-18 (dual side, dual layer). As the nomencla-
ture loosely suggests, five disc capacities are sup-
ported: 4.37, 7.95, 8.75, 12.33, and 15.91 Gbytes
(expressed in 8-bit bytes). When the average data output
bit rate is 4.8 Mbps, the approximate playing times are
DVD-5 (133 min), DVD-9 (241 min), DVD-10
(266 min), DVD-14 (375 min), and DVD-18 (482 min).
DVD manufacturing is similar to CD manufacturing.
Following authoring, disc content is typically imaged
on a hard drive disk, transferred to another medium
such as Digital Linear Tape (DLT), and delivered to the
disc mastering facility. A DLT Type III tape cartridge
can hold up to 10 Gbytes of uncompressed data; with a
transfer rate of 1.25 Mbytes/s, a 135 min program can
be transferred in about 1 hour. A separate DLT is used
for each physical disc layer. Alternatively, other media
such as DVD-R or Exabyte may be used.
A single-layer, single-sided DVD-5 disc uses one
substrate with a data surface and one blank substrate.
Two substrates with data surfaces can be bonded
together to form a single-layer, dual-sided DVD-10
disc; the disc is turned over to access the opposite layer.
The DVD standard allows data to be placed on two
layers in a substrate to create a dual-layer disc that is
read from one side comprising a DVD-9 disc. The
layers are separated by a clear resin and a very thin
semitransparent (semireflective from 25% to 40%) sput-
tered layer of gold or silicon. Both layers are read from
one disc side by moving the objective lens and focusing
the reading laser on either layer. The beam either
reflects from the lower semireflective layer or passes
through it and reflects from the top reflective layer.
Because the SNR and reflectivity of the interior layer
are slightly reduced, the layer uses a faster linear
velocity (3.84 m/s versus 3.49 m/s). Thus the pit length
is longer (e.g., the minimum pit length is 0.44μm
versus 0.4μm). The interior layer thus has less capacity
than the top data layer.
In the manufacture of dual-sided discs, two polycar-
bonate substrates are independently formed and then
bonded together using a hot-melt adhesive or
UV-curable bonding. Dual-layer discs can be formed
from two 0.6 mm substrates; one layer is fully metal-
lized and the other is semireflectively metallized. The
two substrates are then bonded together with a layer of
UV-cured optically clear photopolymer. This technique
can be used to manufacture single-sided discs (such as
some DVD-9 discs). Alternatively, a single-layer
substrate can be coated with a semitransparent layer
followed by a layer of liquid photopolymer that is
molded by a second stamper and hardened by exposure
to ultraviolet light. After the layer is hardened, a fully
reflective metal layer is applied and the substrate is
bonded to a second substrate. This technique is used for
some DVD-9 and DVD-18 discs. Construction of a
dual-layer/dual-side DVD-18 disc is shown in Fig.
30-14.30.6.2 DVD File Format and CodingThe DVD format is fundamentally computer-based with
a file format defined for its applications. In particular, the
DVD specification describes Universal Disc Format
(UDF) Bridge, a file format specifically designed for
optical disc storage. Read-only DVDs (DVD-ROM,
DVD-Video, and DVD-Audio) use UDF for volume
structure and file format, and UDF applies to the
write-once and recordable disc formats. However, appli-
cation-specific parameters are unique to both
DVD-Video and DVD-Audio. UDF Bridge is a simpli-
fied version based on Part 4 of ISO/IEC 13346 and con-
forms to both UDF and ISO 9660 (the file format used in
CD-ROM). UDF Bridge defines data structures such as
volumes, files, blocks, sectors, CRCs, paths, records,
allocation tables, partitions, and character sets, as well as
methods for reading, writing, and other operations. It is a
flexible, multiplatform, multiapplication, multilanguage,
multiuser oriented format that has been adapted to DVD
and is backward compatible to existing ISO-9660 operat-Figure 30-14. Construction of a dual-layer/dual-side
DVD-18 disc.Polycarbonate
Semireflective
layerSemireflective
layer
PolycarbonateReflective layerReflective layerBonding layerLaser beamsLaser beams