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DVD-RAM, DVD-RW and DVD+RW
DVD-RAM, DVD-RW and DVD+RW are re-writable disc
formats with a capacity of 4.7GB per side |
DVD-RAM and DVD-RW are the two official re-writable DVD formats.
Both formats use phase change recording where the active layer is made to change
between amorphous and crystalline state by means of a laser at different power.
The differences between the two formats are shown in the table below.
| Parameter |
DVD-RAM
Ver 1.0 |
DVD-RAM
Ver 2.0 |
DVD-RW
Ver 1.0 |
| Sides |
1 or 2 |
1 or 2 |
1 or 2 |
| Capacity (GB) |
2.6 per side |
4.7 per side |
4.7 per side |
| Recording method |
Phase change
marks |
| Track format |
Wobbled Land
& Groove |
Wobble groove |
| Track pitch (microns) |
0.74 |
0.615 |
0.74 |
| Min pit length (microns) |
0.41 |
0.28 |
0.40 |
| Number of zones |
24 |
35 |
|
| User data rate (Mb/s) |
11.08 |
22.16 |
|
| Caddy |
Yes |
|
| Modulation and error correction |
8 to 16 &
RSPC |
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DVD-RAM
DVD-RAM discs use land/groove recording and Zoned CLV (ZCLV) method instead of CLV, where the angular velocity
continuously changes. Within each zone the data is written/read using the CAV
method, the angular velocity changing from zone to zone to maintain a constant average
linear velocity. The data is written on both land and groove, the address
information being moulded into the disc as pits.
The current specification (version 2.1) is for 4.7GB or
9.4GB (double sided) capacity media (12 cm) which offer over 100,000
recording cycles and a 30-year life or more.
DVD-RW
DVD-RW discs use groove recording offering a 4.7GB capacity per
side and does not need a cartridge. It offers advantages over tape in life
(videotape life is only 15 to 20 years) and the ability to edit home
movies. DVD-RW discs are designed to be compatible with existing players
and drives. Discs are recordable over 1,000 times and they have the same
optical properties as a DVD-9 disc.
DVD-RW discs can be used for videotape
replacement, video authoring and desktop PC backup. Consumer
applications include video recording and home authoring. DVD-RW
discs also offer CPRM copy protection and can include BCA serialisation.
DVD+RW
DVD+RW is a re-writable format introduced in October 2001 by the
DVD+RW Alliance (HP, Philips, Ricoh, Sony, Yamaha, Verbatim/Mitsubishi
Chemical, Dell and Thomson). It is not supported by the DVD Forum.
DVD+RW incorporates lossless linking technology, allowing the drive
or video recorder to accurately stop and start the writing process, or
to replace individual 32kB data blocks. Lossless linking improves
compatibility, performance and ease of use.
DVD+RW discs have a capacity of 4.7 GB and do not need
a cartridge. They offer 1,000 re-writes.
For PC applications, CAV (constant angular velocity) recording
allowsle fast, random access reading of the disc. Multi-session
writing, as for CD-R, allows users to add data at a later date. DVD+RW's
defect management ensures that data is accurately written to and read
from the disc.
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