DVD Demystified

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and the land area. DVD-RW capacity is 4.7 billion bytes (4.37 gigabytes).
DVD-RW media can be rewritten about 1000 times. DVD-RW media typically
comes bare, but it can use the same cartridges as DVD-RAM. See the
following section for details.
Extra information, called a linking sector, is recorded between each ECC
block on the disc. This extra padding allows for “write splices” to occur at the
start and end of each write to the disc. Linking sectors have the same length
and format as a normal sector, but they contain information that identifies
them as not containing user data. A reader must allow for these gaps in the
data by resynchronizing the data clock and otherwise ignoring them.
Unlike DVD-RAM and DVD+RW, DVD-RW is designed for sequential
access, using constant-linear-velocity (CLV) rotation control. Sequential
access improves storage capacity and compatibility. DVD-RW uses a
restricted overwrite mode, which reduces unrecorded gaps on the media.
This is designed to limit extra seeks during recording (other than defect
management sparing) in order to improve real-time recording performance.
The alternative to restricted overwrite mode is sequential recording mode,
which is similar to that of DVD-R. As with DVD-R, border zone recording can
be done to provide compatibility with standard DVD-ROM drives and players.
Defect management is performed in software, using features of UDF 2.0.
For restricted overwrite mode, ECC blocks must be formatted in
advance. Since formatting the entire disc can take a long time (usually
more than an hour), special quick format operations are specified for formatting
small areas at a time and for adding or enlarging border zones.
The power management area (PMA) and recording management area
(RMA) are the same as for DVD-R. The control area is preembossed to prevent
copy protection keys being written. Copy protection is provided by
CPRM (see Chapter 4).
DVD-RAM
Chapter 5
DVD-RAM, officially known as DVD rewritable, is an erasable, rerecordable
version of DVD-ROM. Version 1.0 of DVD-RAM had a storage capacity of
2.58 billion bytes (2.4 gigabytes). It was in increased in version 2.0 to 4.7 billion
bytes (4.37 gigabytes). DVD-RAM media can be rewritten more than
100,000 times. DVD-RAM version 2.0 doubled the recording data rate to
22.16 Mbps (equivalent to 18X CD recording). Version 2.1 added an 80-millimeter
disc size designed for use in portable devices such as digital camcorders.
DVD-RAM uses phase-change (PD) technology with some CD-RW and
MO features mixed in. A wobbled groove provides clocking data with a