Format Confusion

 
 
By Robert Starrett  |  Posted 2003-01-01 Email Print this article Print
 
 
 
 
 
 
 


Format Confusion

All the write-once (R) and rewritable (RW) DVD versions make a daunting puzzle. Pioneer released a DVD-R drive in 1997, but the device wasnt affordable. Rewritable DVD-RAM first appeared in 1998, but its initial iterations werent compatible with computer DVD drives. The DVD-RW standard wasnt completed until early in 2001 and wasnt universally accepted. Most recently, a few notable electronics companies introduced the DVD+RW and, later, the DVD+R formats, which promised greater compatibility with standalone DVD players. To make sense of this mess, lets break it down by drive type and medium.

DVD-RAM drives, much like magneto-optical drives, use a disc enclosed in a cartridge. But standalone DVD players and DVD drives dont accept cartridges, so DVD-RAM discs could not be read in anything other than DVD-RAM drives. This changed with the advent of the Type II DVD-RAM cartridge, which let you remove the disc and insert it into a DVD player or a computer DVD drive. Not all DVD-RAM drives accept Type II cartridges, though, so check the specifications of any units youre considering if youre shopping for this type of drive. The capacity of DVD-RAM media is either 4.7GB or, for double-sided cartridges, 9.4GB.

DVD-RAM cartridges claim to allow 100,000 rewrites. This is great for backup purposes, because you can treat the DVD-RAM drive like any other drive, and you have plenty of room for data. Incidentally, some newer DVD-RAM drives can record to DVD-R, CD-R, and CD-RW discs (without a cartridge). DVD-RAM drives can also play all CD formats.

Industry experts say that DVD-RAM is losing ground to the other rewritable DVD formats, and that it may fade from the market as the competing standards vie for dominance. Moreover, new combination drives support both "dash" and "plus" standards—but not DVD-RAM.

Drives labeled DVD-R/RW record to like-named media and also to write-once and rewritable CDs; they read all CD formats, too. DVD-RW discs allow up to 1,000 rewrites and hold 4.7GB. This format has been around a little longer than its main competitor, DVD+R/RW, and has thus gained wider acceptance in the DVD-authoring and DVD player categories.

DVD-RAM and DVD-R/RW have been approved by the DVD Forum (which includes Hitachi, JVC, Philips, Pioneer, Sony, Toshiba, and many more). But because the group is not a standards-setting body, approval is meaningless in any practical sense. ECMA, the European Computer Manufacturers Association, has approved all DVD–recordable formats, including DVD+R and DVD+RW.

The main developers of DVD+R/RW are HP, Philips, and Sony, who felt that this technology was superior to existing ones (hence the plus sign). The drives record to DVD+R and DVD+RW discs, but not to DVD-R or DVD-RW media. The standard is not endorsed by the DVD Forum. DVD+R/RW media also hold 4.7GB and can tolerate up to 1,000 rewrites. Dash and plus double-sided discs—which you have to turn over—are just becoming available.

Plus drives work at least as well as dash drives, and some features may make them faster and more reliable than their counterparts. For example, DVD+RW drives record at faster rates than most DVD-RW units. Some DVD-R discs can be written at near DVD+R speeds, though, and recently announced DVD-RW models should narrow the speed gap further.

Another difference between dash and plus technologies involves the way the drives spin discs. CD, DVD-ROM, and DVD-RW drives are constant linear velocity (CLV) devices, which maintain constant data-transfer rates when reading discs. These drives rotate discs more slowly when reading near the outside edges, where there is more physical surface in each track. Faster drives use CAV (constant angular velocity), keeping the rotational speed constant and using a buffer to deal with the differences in data readout speeds. CAV is particularly important for PC users, as it allows for higher-speed DVD and CD reading. DVD+R/RW drives support both CLV and CAV. In addition, plus drives dont require session closing and finalization when burning discs. All this translates to a slight speed advantage for DVD+R/RW.

Now lets throw in a fourth drive type to complete the picture: the combination drive. This type records to all of the dash and plus formats (but not to DVD-RAM) in addition to CD-R and CD-RW. The Sony DRU-500A ($350 street) is one such drive.



 
 
 
 
 
 
 
 
 
 
 

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