DVD-ROM and CD-R: the compatibility question answered

Emedia Professional, March, 1998 by Hugh Bennett

Although many first-generation DVD-ROM drives came to market unable to read CD-R discs, astute hardware manufacturers have responded to the concerns of the market and mobilized a tremendous industry effort to ensure that all their current products offer CD-R compatibility.

As the first generation of DVD-ROM drives ushered in a brand-new day in high-density optical media storage, the same drives seemed to spell doom for die-hard CD-R users, who harbored a well-founded fear that they might have to abandon their investments in CD-R hardware and media and migrate to the new technology. Abandoning the efforts they had already made with CD-R or continuing on with both existing and new technology by means of two separate hardware devices hardly represented an attractive solution.

Given the unique capabilities of CD-R and its established and projected popularity, incompatibility between DVD and CD-R would be unthinkable to most users. Although many first-generation DVD-ROM drives came to market unable to read CD-R discs, astute hardware manufacturers have responded to the concerns of the market and mobilized a tremendous industry effort to ensure that all their current products offer CD-R compatibility. According to Jacques Heemskerk, Program Manager for Philips Electronics NVs Philips Components, "CD-R is so widely available now you can't sell DVD-ROM without being able to read it. You really can't claim to be CD-compatible unless you are CD-R-compatible."

The same holds true for much-anticipated DVD-RAM drives, which will follow the specification for rewritable DVD approved by the DVD Forum in mid-1997. Although no DVD-RAM drives were shipping at press time, expectations remained high for the new models, a smattering of which are scheduled to ship in the first months of 1998. And since part of that expectation--at least in the minds of DVD-ROM/RAM manufacturers like Toshiba America Information Systems, Inc. and Hitachi America, Ltd.--is for DVD-RAM drives to replace read-only DVD-ROM drives over time, it's good news that the manufacturers plan to take CD-R along for the ride into high-density rewritable nirvana. DVD-RAM's triumph is not a done deal at this point, but its proponents are clearly resolved to include CD-R-reading capability in the very first DVD-RAM drives, as are supporters of potential competing specs like DVD RW when their drives debut.

But whether ROM, RAM, or RW, the message issued with the second wave of DVD-ROM drives will hold true for some time: CD-Xs got a future with DVD.

MAKING DVD CD-R-SAFE: THE TWO-LASER SOLUTION

Since CD-R discs were never designed to be read at wavelengths shorter than 780nm--and certainly not at the 650nm wavelength used for DVD--Philips Electronics in 1996 originally proposed that the solution to the compatibility problem was to create a new type of upwardly-compatible CD-R Type II disc capable of being read at both 780nm and 650nm wavelengths. But developing CD-R Type II proved a formidable technical challenge. Describing his company's efforts to develop a CD-R Type II disc, Taiyo Yuden, Inc. general manager for new product planning Tad Ishiguro says the company "found that it was not difficult to achieve the specification proposed by Philips at 650nm by changing organic dye components or introducing phase change material. However, it was extremely difficult to maintain the recordability and playability with all the CD-R recorders and CD players in the market."

As a result of the technical problems and runaway success of existing CD-R, the idea of a Type II disc was abandoned in 1997 in favor of a plan to create DVD-ROM drives capable of generating both 780nm and 650nm wavelengths for reading both DVD and CD-R. As the technological obstacles have been overcome, most major DVD drive manufacturers have chimed in with CD-R-reading DVD-ROM drives that net the same result, but are achieved through a handful of different technological strategies. Sony Electronics, Inc., for example, uses two distinct optical pickups to read 780nm CD-R discs and 650nm DVD-ROM discs, while Samsung pioneered the single-lens, double-duty method with its first dual-read DVD-ROM drive. Others taking the CD-R/DVD-ROM-compatible drive plunge are key DVD players Toshiba, Hitachi, and Matsushita Electronic Industrial Corporation.

Sony Electronics: The First Paired Pickups

Without a doubt, the company that took the lead in the area of CD-R hardware compatibility was Sony Electronics. In July 1996, Sony announced two twin-laser CD-R-compatible DVD optical pickups, the KHS-180A, offering 635nm and 780nm wavelengths, and the KHS-18013, employing 650nm and 780nm wavelengths.

Formally dubbed the "Dual Discrete Optical Pickup," the new pickups achieve backward-compatibility with existing CD and CD-R discs using a two semiconductor design that joins Sony's existing 8X 780nm laser coupler with either a 635nm or 650mn pickup. Except for the objective lens, the laser coupler integrates all the components of a single-beam 780nm pickup (photo detector, micro prism, 780nm laser diode, and integrated circuit) into a tiny bundle small enough to be fastened to the larger DVD pickup. And for dealing with the unique characteristics of DVD discs, the pickup employs a discrete DVD optical system with its own components (photo detector, objective lens, collimator lens, beam splitter, 635 or 650nm laser diode) and separate light path.