DVD Formats
DVD FORMATS
CD-Recordable discs (CD-R) were introduced
in 1988 and CD-RW (the re-writable version) was introduced about 15
years after the first read-only CD was launched.
In addition, both write-once and
re-writable DVD discs are also available.
There are several different formats.
- DVD-R
discs are write-once discs with a capacity of 4.7GB per side.
Two versions have been defined: DVD-R for Authoring and DVD-R
for General use. Note that copy protected content cannot be
written to DVD-R discs.
- DVD-RAM
discs are re-writable discs with a capacity of 4.7GB per side
for computer data storage and archive applications, although
this format is also used in some DVD video recorders.
- DVD-RW
discs are re-writable discs with a capacity of 4.7GB per side
for consumer applications such as video recording.
- DVD+RW
and DVD+R
discs are not officially part of the DVD family, but are similar
to the corresponding DVD-RW and DVD-R for General formats.
Both recorders and discs for these
formats are available and include PC drives, video
recorders and camcorders.
Compatibility is an issue, as not all formats will play on existing
DVD players and DVD-ROM drives.
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DVD
Recordable Formats Guide
DVD
TECHNOLOGY
DVD and CD-ROM's
serve the same purpose, but in different ways.
DVD's and CD's have
the same physical characteristics, but are internally different.
They are also both read the same way, using pits and lands to
reflect a laser.
A DVD is
exactly the same size (physically) as a CD, but can store seven
times the data that a CD-ROM can. The disk itself is 120mm in
diameter and 1.2mm thick. It can store 4.7 gigabytes while CD-ROM
can only hold up to 800 megabytes.
DVDs also come in several versions:
- DVD 5 is
a single sided, single-layered disk with a capacity of 4.7 GB
- DVD-9 is
a single sided, double-layered disk with a capacity of 8.5 GB
- DVD-10 is
a double sided, single-layered disk with a capacity of 9.4 GB
- DVD-18 is
a double sided, double-layered disk with a capacity of 17 GB.
- HD-DVD stores 20+ GB and
plays using a blue laser for higher disc capacity needed for
HDTV.
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- There are also many physical
formats to DVDs:
- DVD-ROM is a high capacity data
storage medium
- DVD-Video is a digital storage
medium for a feature-length motion picture
- DVD-Audio is an audio-only
storage format, similar to CD-Audio
- DVD-R is similar to a CD/R
which offers a write-once, read many storage format
- DVD-RAM was the first re-writable
(erasable) DVD.
- DVD-RW offers a re-writable
format
The tracks
in a DVD are placed much closer together than a CD with the pits
and lands also being much smaller, thus allowing for more data
storage. A DVD also allows information to be scanned from more
than one layer of a DVD by changing the focus of the read laser.
Instead of using an opaque reflective layer is uses a translucent
layer with an opaque reflective layer behind carrying more data.
However, this does not double the capacity of the disk because the
second layer cannot be as dense as the single layer.
An
interesting feature of DVD is that the disks' second layer can be
read from the inside of the disk out, as well as from the outside
in. In an ordinary CD, the data begins reading from the center
(the hub) of the disk and goes out.
A DVD also
allows for double-sided capacity. This means that data can be
stored on both sides of the disk. To facilitate the focusing of
the laser on the smaller pits, manufactures used a substrate
thinner than that used in CDs, thus reducing the depth of the
layer of plastic the laser has to travel through to reach the
pits.
Because of this, the resulting disk was only 0.6mm thick,
which was too thin to remain flat and withstand handling. The
solution was to bond two disks back-to-back, effectively doubling
the potential storage space.
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