The Difference Between DVD- & DVD+

The Difference Between DVD- & DVD+ thumbnail
DVDs emerged in the late 1990s as an alternative to videotape and laserdiscs.

When it comes to DVDs, the variety of formats can seem overwhelming. Although hybrid DVD drives can handle most disks, it's still helpful to know what the various format designations mean, particularly if you burn your own DVDs or need to consider what disks to use on older generation players.

  1. How a DVD Works

    • DVD originally stood for Digital Video Disk when DVD was a read-only movie playback medium. The acronym was later amended to Digital Versatile Disk as record and rewrite functions were added to DVD capability. Both CD and DVD technologies use a laser to read pits burned into a disk's surface. A DVD's pits are much smaller than those on a CD, allowing for approximately 5 to 10 times more capacity on a DVD. DVD lasers can read the larger pits of a CD, but a CD laser cannot read a DVD.

    The DVD-R Format

    • In the late 1990s, manufacturers developed proprietary ways to use the DVD format, leading to a situation reminiscent of the videotape format war between VHS and Betamax in the 1980s. DVD-R was introduced in 1997 by Pioneer, and the format was supported by manufacturers such as Toshiba, Hitachi and Panasonic. The DVD-R format uses marks called land prepits to identify where the laser is scanning on the disk surface. These prepits allow the DVD system to move accurately between menus and chapters or other data burned on the DVD.

    The DVD+R Format

    • Manufacturers Sony and Philips were behind the DVD+R format, released in 2002. Instead of prepits on the DVD surface, the laser's wobble frequency is measured to determine where the laser is and how it should move between data locations on the disk. The format developed from manufacturers who did not want to pay royalties for the rights to use Pioneer's DVD-R format. Fortunately, unlike the result of the videotape format battle, multi-format players emerged that could handle both formats.

    RW Technology

    • Since the greatest difference between formats is how the laser's location is tracked, other DVD functions remain consistent across formats. Recordable DVDs start with a thin layer of dye that is etched by the drive's laser, simulating a pit when the read laser scans the surface. In rewritable disks, the dye layer is replaced by a metal layer. At its highest power, the laser produces a random, formless pattern on the metal layer. At medium level, the laser can write crystalline marks on the metal layer, which the laser at low power reads to play video or provide data. The crystalline writing can be reversed into the amorphous pattern without damaging the DVD's surface.

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References

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