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(No.1 High-Tech News Site in Japanese)

News from NET and COM '99

  • Rewritable DVDs Enter 4.7GB Era With Major Compatibility Issues
  • February 8, 1999 (TOKYO) — Rewritable DVD discs, which comprise a new type of storage media with different formats, will be shipped from this spring, even though problems of compatibility are unresolved.
    Makers of media products have been arguing over issues relating to international standards for DVD discs. The SD group led by Toshiba Corp. and Matsushita Electric Industrial Co., Ltd., and the MMCD group including Sony Corp. and Philips Electronics N.V. of the Netherlands argued over the process of standardizing the basic DVD format in 1995.

    The arguments heated up when they planned to introduce rewritable DVD discs (See table.).

    Sony will start selling a DVD+RW disc capable of storing 3.0GB of data on each side, from this spring. The DVD+RW format is not compatible with the DVD-RAM format that has been defined by the DVD Forum.

    “The DVD+RW format is an arbitrary standard proposed by Sony, and thus the DVD-RAM group is not responsible for supporting it,” said Kazuo Shigematsu, chief engineer and DVD-RAM Project leader of Hitachi Ltd.’s Image & Information Media System Division.

    The DVD-RAM group will expand the existing standards of 2.6GB up to a single-sided storage capacity of 4.7GB. It will firm up DVD Forum standards for DVD-RAM discs with the same storage capacity as DVD-ROM discs, as early as this spring.

    Also, makers of media products, including Hitachi, Toshiba and Matsushita, will start shipping the new products in the second half of 1999.

    Sony has no plan to enable DVD-ROM drives to play back DVD-RAM discs, according to Hajime Hattori, planning section manager of the data storage division at Sony Corp.’s Computer Peripherals and Components Co.

    Neither Format Compatible with DVD-ROM Drives

    DVD-RAM discs and DVD+RW discs, which are featured as rewritable DVD media, have formats that are different from that of DVD-ROM discs. This is because the new discs are designed for recording sequential images or music as well as for personal computers, targeting easy data handling.

    Therefore, a DVD-ROM drive needs a change in firmware to play back either a DVD-RAM disc or a DVD+RW disc.

    Rewritable DVD discs and DVD-ROM discs differ in their data formats as well as in reflectance of media. Thus, a gain adjustment is necessary for DVD-ROM drives to read some rewritable DVD media. Also, DVD-RAM discs and DVD-ROM discs use different positions to store data.

    To move a laser head precisely to the positions where data is stored, a rewritable DVD disc has grooves that are convex against the laser head. It also has concave parts, called lands, against the laser head.

    The DVD-RAM format stores data on both grooves and lands to raise the storage capacity. When a laser head writes data, a groove or a land is alternatively fed as the disc make a complete revolution. When a DVD-ROM drive reads that medium, an additional circuit is necessary, to adjust reflected signal levels as the disc rotates.

    However, the DVD+RW format uses only grooves to store data, as do the formats employed for CD-R or CD-RW discs. That means no additional circuit is needed for that format.

    The DVD-RAM group expressed concerns that the storage capacity of 4.7GB, equivalent to that of DVD-ROM media, is difficult to achieve without using both grooves and lands, if current media technology and a laser wavelength of 650nm are utilized, as noted by Hitachi’s Shigematsu.

    Sony, a DVD+RW group member, is developing a DVD+RW disc with a storage capacity of 4.7GB. It will be commercialized as early as 2000, Hattori said. Thus, DVD+RW media with 4.7GB in storage capacity will be marketed about a year after the shipments of DVD-RAM discs.

    DVD-RW Media Aim at Market for Video Recorders

    DVD-RAM and DVD+RW discs have data storage and data processing features. However, Pioneer Electronic Corp. is developing DVD-RW media featuring compatibility with DVD-ROM discs.

    DVD-RW drives can play back DVD-ROM discs, and they use the same format as the write-at-once media, the DVD-R disc.

    Unlike DVD-RAM discs, DVD-RW discs do not have data-save areas. Their overwrite cyclability (read/write) is just over 1,000 times, or far fewer than those of DVD-RAM or DVD+RW discs. The latter two have overwrite cyclabilities of more than 100,000 times.

    The DVD Forum is firming up standards for the DVD-RW format, assuming that DVD-RW discs will be suitable for authoring tools for DVD-ROM discs. A Pioneer official said that although the company has not yet decided on a shipping date, it may start shipping the products in 1999 because it has already finished developing basic technologies.

    DVD-RW drives use a laser with a short wavelength of 635nm to write data. The large storage capacity of 4.7GB has been achieved using that short wavelength.

    However, components makers have not completed the production technology for lasers with a wavelength of 635nm. Poor yields are pushing the prices up.

    A DVD-R drive with a 635nm laser, the same wavelength as DVD-RW drives, is priced at more than 1 million yen (US$8,920), while a DVD-RAM drive with a 650nm laser is priced at about 100,000 yen.

    Because of the high prices, DVD-RW drives cannot yet be called consumer products.

    Akiyoshi Inoue, general manager of the recording & mechanical engineering department of Pioneer’s R & D Center, noted that at least two years will be needed before the prices drop to the levels of DVD-RAM drives.

    Some are skeptical about the existence of DVD-RW media in a market where DVD-RAM media have already been introduced.

    However, Inoue said the era envisaged by DVD-RAM media, where images and data are integrated, will not arise if the storage capacity remains at just 4.7GB. Thus, the compatibility with DVD-ROM discs is important for the DVD-RW media, he said.

    At this stage, when DVD media aren’t yet disseminated, a strategy to push DVD-RW media as video recording discs may be worth considering, industry analysts said.

    Table: Main specifications of rewritable DVD media

    Name of standard


    DVD-RAM ver.2.0



    DVD-ROM (ref.)

    Company/ Organization developing

    DVD products

    DVD Forum

    DVD Forum


    Pioneer Electronic

    DVD Forum

    One-side capacity (GB)






    Places of data storage

    land and groove

    land and groove



    Laser wavelength (nm)







    more than 15%

    more than 15%



    18-30% (double layers)/ 45-85% (single layer)

    Track pitch (micron meter)






    Rotational control



    CAV or CLV



    Overwrite cyclability (Read/ Write


    more than 100,000

    more than 100,000

    more than 100,000

    more than 1,000

    Shipment date

    Apr. 1998

    2H 1999

    Spring 1999


    Dec. 1996

    (return to news)

    (Tadashi Nakamichi, Staff Editor, Nikkei Byte)

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