1152 Chapter 30
ally compatible and can be played in many DVD-ROM,
DVD-Video and DVD-Audio players.
The DVD-RW format allows data rewriting; the
specification is an extension to the DVD-R format.
Discs use a phase-change recording mechanism and a
multilayer disc structure with dielectric layers above
and below the recording layer. Data is recorded into a
wobbled pregroove with CLV; relatively large data
blocks are written. The recording layer may use a silver,
indium, antimony, and tellurium compounded layer and
allows perhaps 1000 writing cycles. Unlike
dye-polymer technologies, phase-change recording is
not wavelength-specific.
The DVD-RAM (random access memory) is a true
random-access, nonsequential storage format. It uses a
phase-change recording mechanism and a wobbled land
and groove disc design. Data may be recorded on both
planar surfaces of the groove and land; a wider track
pitch is employed. This technique doubles disc
capacity; deep grooves with steep walls are used to
avoid crosstalk interference between adjacent data.
Servos are used to switch the pickup’s focus between
the groove and land area on each revolution, and the
tracking signal is inverted when the switch occurs.
Discs contain preembossed pit areas (for every 2k
sector) containing addressing header information and
zoned constant linear velocity rotational control.
DVD-RAM provides advanced error correction and
defect management features. A disc allows perhaps
100,000 rewrite cycles and offers a high degree of
stability for archiving integrity.
DVD+RW is a rewritable format that uses
phase-change media, a wobbled pregroove, and CAV or
CLV rotation, for either raw data transfer or faster data
access. Data is recorded in the pregroove, not on the
land. Data addresses are represented by modulation of
the pregroove; this necessitates somewhat larger writing
blocks. Over 100,000 rewrite cycles are possible. Both
sequential and random access recording are supported.
30.10 HD DVD Format
New high-density disc formats are under continual
development. HD DVD (high definition DVD) is one
such format that can carry motion pictures in high-defi-
nition form, with picture quality greater than that of
standard-definition DVD, and providing broadcast DTV
high-definition quality. In addition, HD DVDs employ
content protection that is more robust than that currently
used in DVD.
The HD DVD format uses a 405 nm blue-violet laser
and numerical aperture (NA) of 0.65. As with the DVD
format, 12 cm diameter discs are formed from 0.6 mm
substrates bonded together; data can be placed on one or
both interface layers. Track pitch is 0.40μm. A HD
DVD-ROM holds 15 Gbytes on a single-layer disc,
30 Gbytes on a dual-layer disc, and 51 Gbytes on a
triple-layer disc. A dual-side, single-layer disc holds
30 Gbytes and a dual-side, double-layer disc holds
60 GB. The structure of the HD disc is shown in Fig.
30-18. The single-speed transfer bit rate is 36 Mbps,
and the double-speed bit rate is 72 Mbps. HD DVD
movies have a maximum data bit rate of 36.55 Mbps
(1×); maximum video bit rate is 28.0 Mbps. HD DVD
supports the ISO 9660 and UDF optical disc file
formats. HD DVD players can also play CDs and
DVDs. HD DVD drives are available for the Xbox 360
and computer applications.The mandatory video codecs for HD DVD players
are VC-1 (SMPTE 421M), MPEG-4 H.264 Advanced
Video Codec (AVC), and MPEG-2. In practice, the
majority of movie titles are coded with VC-1 at 1080p,
with a minority coded with AVC. The HD DVD format
supports a range of video resolutions, from low-resolu-
tion formats such as CIF and SDTV, to high-resolution
formats such as HDTV at 720p, 1080i, and 1080p.
The mandatory audio codecs for players are Dolby
Digital, Dolby Digital Plus, Dolby Digital EX, Dolby
TrueHD (using MLP), DTS, and linear uncompressed
PCM. Optional audio codecs include DTS-HD Master
Audio and DTS-HD High Resolution Audio. Using
these codecs, HD DVDs can contain up to eight chan-
nels of 24-bit/96 kHz audio, or two channels of
24-bit/192 kHz audio.
HD DVD optionally allows use of the Advanced
Access Content System (AACS) for digital rights
management, copy protection and content distribution
control. AACS uses the Advanced Encryption StandardFigure 30-18. HD DVDs use two 0.6 mm substrates
bonded together. A single-side disc is shown, but dual-side
discs can be used.1.2 mmSurface velocity = 6.6 m/sNA = 0.65L = 405 mm0.6 mm0.6 mm1.0 mm