April 14, 1997 -- The ten companies comprising the DVD Forum today announced a major milestone to further expanding DVD's potential as a large-capacity storage media, with the finalizing of specifications for rewritable DVD, DVD-RAM, and a write-once DVD, DVD-R.

The specifications were optimized following intensive consideration of industry requirements, and with full consideration for compatibility with, and the future expandability of, the overall DVD format. The Forum will issue the Format Books detailing the specs as version 0.9, in mid April. They will be made available to all interested parties, and will be further promoted in a series of conferences in Japan, the US and Europe from late April on.

The huge capacity of DVD positions DVD-RAM to play a key role as a rewritable medium for computers, allowing users to store and modify data in addition to just playing back pre-recorded data. That same capability also positions DVD-RAM to extend into other areas in the future, including storage of moving images. DVD-R, a write-once disc, is ideal for recording archival data. It can also be used as a test disc for developed applications, since it can be played on a standard DVD-video player.

The main characteristics of the discs are as follow:

DVD-RAM

1. Adoption of the wobble land groove recording method, which records signals on both the lands -- the area between grooves -- and the grooves formed on the disc. Clock data is formed on the track wobbles at the disc manufacturing stage. The capacity of a single-sided DVD-RAM disc is 2.6 gigabytes, twice that for a double-sided disc.

2. Phase-change recording. Signals are recorded to a film, which the DVD-RAM drive's laser transforms from a crystalline to an amorphous state. The signal is read as the difference of the laser reflection rate between the two states. Phase-change recording realizes excellent read output.

3. Modulation and error correction codes are the same as for DVD-Video and DVD-ROM, assuring compatibility with other DVD formats.

4. At the manufacturing stage, the disc's positioning accuracy is enhanced by including position data (address signal) in the pits formed on the lands and grooves, by laying down the tracks so that they meander slightly right and left of true, and by including clock data in the meanders.

5. Disc cartridges will be provided for both single- and double- sided discs. Double-sided discs must be needed with the cartridge, but single-sided discs can be taken out from the cartridge.

DVD-R

1. This write-once optical-disc medium has a single-sided storage capacity of 3.95 gigabytes, about 6 times that of a CD-R, and double that for a two-sided disc.

2. A simple and system configuration in which the optical mechanism records to an organic dye recording layer. The organic dye method also allows the low material cost.

3. Modulation and error correction codes are the same as for DVD-Video and DVD-ROM, assuring compatibility with other DVD formats.

4. High precision data recording is possible since the disc's position data (address signal) is pre-engraved in the pits at the disc manufacturing stage. The disc's tracks meander slightly right and left, and clock data is located in the meanders.

Outline of specifications

DVD-RAM

DVD-R

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For further information, please contact DVD Forum:+81-3-5444-9580