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The duel of the dual-layer DVD formats

The DVD+RW camp is expected to be first with products that nearly double the amount of data held on one disc--but that achievement may not win the format war.

One side of the ongoing recordable DVD format battle is expected to be first with products that nearly double the amount of data held on one disc. But that victory may not put an end to the feud.

The DVD+RW camp, which includes Hewlett-Packard, Dell and Philips, plans to put so-called "double-layer" DVD recording devices on the market by next spring. Discs on these systems are expected to hold 8.5GB, or four hours of DVD-quality video (16 hours of VHS-quality video). That's about the same amount as the DVDs studios use to issue movies.

But the so-called "dash" camp promoting the DVD-R and DVD-RW formats also is working on dual-layer recording, which involves writing data on two separate surfaces, layered like coats of paint, on a DVD. And unlike in the videotape-standard battle between VHS and Betamax, "plus" and "dash" may be able to coexist for some time to come, observers say.

"I would put my money on the plus camp" in bringing out dual-layer DVD recording first, said Pete Gerr, an analyst with research firm Enterprise Storage Group. But when it comes to the overall format struggle, "it continues to be a skirmish for as long as Pioneer wants to stay in it," Gerr said. Pioneer is a major advocate of the dash format.

"I do believe that the plus guys are going to get there first," said Robert DeMoulin, marketing manager for branded optical products at Sony Electronics. Sony, like some other manufacturers, makes DVD recorders that combine both plus and dash technology.

DeMoulin pointed out there are plenty of older dash recorders on the market. "I just don't see that the dash format is going away anytime soon," he said.

Pluses and minuses
The skirmish began a few years ago, when a group of companies did not like the recordable DVD technologies developed by the DVD Forum standards body. The DVD Forum approved formats called DVD-RAM and DVD-R, for write-once recording. Later, the DVD Forum added the DVD-RW rewritable standard for the ability to record, erase and record again on the same disc.

The dissident companies formed the DVD+RW Alliance, which put out its own technology for write-once and rewritable recording. As a result, seemingly countless recordable drives and disc media types are on the market, creating potential confusion for consumers. For example, a DVD-R/-RW drive cannot record on +R or +RW discs. In theory, discs that are recorded using +R, +RW, -R and ?RW media all can be read by DVD players. But a recent government study found that DVDs and DVD drives are compatible only 85 percent of the time.

The move from single-layer to double-layer recordable DVDs, rather than resolving the fight, just extends it to another battleground.

Slow burn
Single-layer recordable DVDs--or digital versatile discs--hold up to 4.7GB and can be used to store data or up to two hours of digital video. Their popularity is growing quickly. The number of write-once recordable DVDs sold worldwide is expected to climb from 55 million in 2002 to more than 300 million this year, according to research firm Santa Clara Consulting Group.

Retail movies sold on DVDs typically come with data written on two layers. But the commercial process involves "stamping" the discs rather than burning spots with a laser, the method used by DVD writers. Dual-layer recording has not been available to the average consumer in the past. The new technology will give consumers the ability to cram much more data onto discs burned at home.

"Dual layer is a great sort of incremental turn of the technology crank," Gerr said.

Both the plus and dash groups have created prototypes of dual-layer recording technology. Neither side has an official specification, but the plus group has a more aggressive schedule. It has finished writing up the details of a dual-layer, write-once standard for recording data at up to 2.4 times the normal playback speed (2.4x).

Dual-layer DVD recorders slated for PC use are expected to emerge by spring, with dual-layer recorders targeted at the consumer electronics market available later in the year, according to Hans Driessen, global communications manager for Philips' Optical Storage division.

Dual-layer DVD-R products are slated to come out sometime next year, said Andy Parsons, senior vice president in the business solutions division of Pioneer Electronics USA. But he said dual-layer recording, no matter what the format, faces hurdles. One is the importance of fully recording both layers of a dual-layer disc, he said. If that doesn't occur, Parsons said, some DVD players might behave unpredictably, for instance by causing a momentary interruption of the program.

Speeds and feeds
Fully recording an 8.5GB dual-layer disc could increase the time needed to make a recording, according to Parsons. "That's what we're thinking about now," he said. "One must be careful not to rush things to market.

The dual-layer DVD+R specification does not require the entire disc to be recorded. Philips' Driessen said that if one layer of a dual-layer DVD+R has a recorded signal at a particular point on the disc, the other layer must have a matching signal; otherwise, a player may detect an error. For example, if one layer has 4GBs of data recorded, the other layer must have 4GB as well. But he said blank space may be left at the edge of the DVD without any playback problems.

Arranging for both layers to be recorded in equal amounts is relatively easy in the case of data files of a known size, Driessen said. When a user records a television broadcast of unknown length, however, the drive may need to add "dummy" data in order for the disc to be readable in DVD players. This could mean a finalization process of up to 25 minutes, Driessen said. "Future write speed improvements (such as 4x) will reduce this finalization time," he said.

The dual-layer DVD+R recording prototype created by Philips and media-maker Mitsubishi Kagaku Media uses focused light to mark areas on two dye surfaces stacked on top of each other. For each dye layer, reflective material sits underneath to send back light to the lens, which interprets the signal. One challenge is getting light to stop and record on the closest layer, and also to pass through it to record data on the subterranean surface.

Plus and dash can each claim victory in some regard. Sales of recordable DVD media using the plus format increased from 2 percent of the U.S. retail market in July 2001 to 55 percent in July 2003, according to market research firm NPD Group.

But the dash format has been holding steady around the world. According to Santa Clara Consulting Group, the combined factory sales of ?R and ?RW blank media amounted to 61 percent of the total worldwide market share in the third quarter. DVD+R and +RW blank media accounted for 37 percent, while DVD-RAM media sales made up 2 percent. Dash media's worldwide market share hovered at about 60 percent for the first three quarters of the year, according to the research firm.

The end result will likely be uneasy coexistence. Parsons said he used to think the dash forces would triumph, but no longer. The term "victory" isn't relevant anymore, he said, because the price of dual-format drives soon will be close enough to that of single-format drives that few people will choose just one format. Pioneer has shifted to drives that can work with both plus and dash formats.

"I think they're both going to coexist for a long time," he said. "There's room for everybody."