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A DVD-Recordable or DVD-R (pronounced "DVD Are" or "DVD Dash Are") is an optical disc with a larger storage capacity than a CD-R, typically 4.7 GB (4.38 GiB) instead of 700 MiB, although the capacity of the original standard was 3.95 GB. Pioneer has also developed a 8.54 GB dual layer version, which appeared on the market in 2005. A DVD-R can be written to only once, whereas a DVD-RW (DVD-rewritable) can be rewritten multiple times.
The DVD-R format was developed by Pioneer in autumn of 1997. It is supported by most DVD players, and is approved by the DVD Forum.
A competing format is DVD+R (also DVD+RW for the rewritables). Hybrid drives that handle both formats are often labeled DVD±R and Super Multi (which includes DVD-RAM support) and are very popular.
The larger storage capacity of a DVD-R compared to a CD-R is achieved through smaller pit size and smaller track pitch of the groove spiral which guides the laser beam. Consequently, more pits can be written on the same physical sized disc. In order to write smaller pits onto the recording dye layer (see CD-R) a red laser beam with a wavelength of 650 nm (for general use recordable DVD) is used in conjunction with a higher numerical aperture lens. Because of this shorter wavelength, compared to CD-R, DVD-R and DVD+R use different dyes to properly absorb this wavelength.
DVD-R discs are composed of two 0.6 mm polycarbonate discs, bonded with an adhesive to each other. One contains the laser guiding groove and is coated with the recording dye and a silver, silver alloy or gold reflector. The other one (for single-sided discs) is an ungrooved "dummy" disc to assure mechanical stability of the sandwich structure, and compatibility with the compact disc standard geometry which requires a total disc thickness of about 1.2 mm. Double-sided discs have two grooved, recordable disc sides, and require the user to flip the disc to access the other side. Compared to a CD's 1.2 mm of polycarbonate, a DVD's laser beam only has to penetrate 0.6 mm of plastic in order to reach the dye recording layer, which allows the lens to focus the beam to a smaller spot size, which is key for writing smaller pits.
In a DVD-R, the addressing (the determination of location of the laser beam on the disc) is done with additional pits and lands (called land pre-pits) in the areas between the grooves. The groove on a DVD-R disc has a constant wobble frequency used for motor control etc.
Capacities
DVD-R 4.37 gig (4.70 BB)
DVD-RW 4.37 gig (4.70 BB)
DVD+R 4.37 gig (4.70 BB)
DVD+RW 4.37 gig (4.70 BB)
Other capacities (mini-disks, dual sided disks, dual layered disks, etc) can be found here:
A DVD advertised as 4.7 GB may hold less than that because manufacturers quote the capacity of a writable DVD disc in decimal (base 10) rather than binary (base 2) notation. This can be confusing. While a 4.7 GB DVD technically can store 4.7 billion "base 10" bytes [4:700,000,000 bytes ? 1000 = 4,700,000 KB ? 1000 = 4,700 MB ? 1000 = 4.7 GB], in binary notation (as is typical with CD-R, CD-RW and most operating systems) the same disc has a capacity of roughly 4.38 GB [4:700,000,000 bytes ? 1024 = 4,589,844 KB ? 1024 = 4,482.27 MB ? 1024 = 4.38 GB]. More about this here: |
