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DVD-R and DVD-RW
The 4.7 GB
DVD-R specification was divided and published as two specifications (DVD-R
for Authoring version 2.0 and DVD-R for General version 2.0), out of
concern for copy protection issues. The former specification is restricted
to professional authoring applications, while the latter specification is
available for general consumer applications. The DVD-RW specification was
also designed for consumer applications, and was revised from version 1.0
to version 1.1 to perfect its copy control mechanisms. At the same time,
playback compatibility with DVD-ROM was also improved.
Blank disc structure
DVD-R
for General, for consumer applications, and the DVD-RW discs have the same
structure. That is, the recording laser wavelength and distribution of
recording addresses included in the land pre-pit data are the same, and
both require playback-only areas (areas which cannot be written) for use
in preventing the recording of copy-protected data. Further, these discs
contain an area near the center of the disc for (optional) NBCA copy
generation management data.
The main difference between these and DVD-R for Authoring is in
whether or not copy management mechanisms physically exist on the disc.
The professional and consumer discs also use different laser wavelengths
and addressing schemes so that the each types of disc is not compatible
with the other style of recorder.
The means of creating a read-only
region on the surface of the recording disc is currently different for
DVD-R and DVD-RW. Since DVD-R for General is a write-once medium, the disc
manufacturer creates the read-only area by writing to that area as part of
the manufacturing process.
DVD-RW, on the other hand, is a rewritable
medium. In DVD-RW, the read-only area is pre-recorded with embossed pits.
The quality of the signal read from the embossed pits was not specified in
the DVD-RW version 1.0 specification. In revising the specification to
version 1.1 it was determined that to complete the copy management
mechanism that signal quality should follow suit with that of the DVD-ROM
specification. As a result, the modification to the specification also
helped maintain compatibility with DVD-ROM discs.
Structure of Blank
Discs
Copy management technology
Consumer-oriented
DVD-R for
General discs and DVD-RW version 1.1 discs are provided with a copy
management mechanism that exists physically on the disc.
To begin with,
each DVD specification provides a mechanism for recognizing the recording
media, and this is common to the entire DVD family. That is, each disc
contains a flag called Book Type which indicates to which specification
the disc is compliant. Recordable DVD media have a particular wobbling
track, which is used as a means to recognize the recordable media.
Detection of this wobbling track allows the player to reject media with an
illegal Book Type; that is, media that has been recorded
improperly.
Besides this, discs also are specified to have a read-only
area, as was described above, as another mechanism for preventing the
recording of copy-protected information.
In DVD-R for General and
DVD-RW version 1.1, by recording specified data (a Media Block Key, or
MKB) to this read-only area, and by further adding a bar code style signal
(called NBCA) to the disc's inner tracks, allows the disc to support a
copy generation management scheme (with support for copy-once media)
called Content Protection for Recordable Media, or CPRM. This additional
generation management information is placed on the disc by the disc
manufacturer, and is an optional feature of the specifications.
Copy Management Structure for
the Writable DVD Specifications
DVD-R and DVD-RW are recordable
and re-recordable DVD standards recognized by the DVD Forum, defined in
accordance with the basic concept of providing compatibility with
read-only discs.
As applications for these recordable media, the DVD
Forum has established the Video Recording format, which provides excellent
support for features such as video editing, and the DVD Video format (for
non-copy-protected data only), which is primarily concerned with providing
compatibility with the existing DVD-Video specification. These
specification are available today for use in certain applications.
The
DVD-R and DVD-RW specifications were promulgated somewhat later than the
read-only specification, and as a result there are some compatibility
issues with some of the earlier DVD players and drives. (For example, some
players cannot recognize DVD-R/RW discs because the aforementioned Book
Type flag is different from those of ROM discs, or because DVD-RW discs
are single-layer discs but have the same reflectivity as dual-layer
discs.) Recently, however, as a result of increased recognition of these
specifications, standardization efforts such as RWPPI (the RW Products
Promotion Initiative), and due to continuing efforts by manufacturers to
improve product quality, compatibility problems and user inconveniences in
the market should be considerably reduced.
Columbia ISA
Empowering consumers thru information
[email protected]
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