Since the Blu-ray announcement in February, Toshiba, the chair company of the DVD Forum, has insisted that the next-generation disk system should be discussed within the forum. But the Blu-ray Disc founders have not formally proposed their format to the DVD Forum, said a spokesman for a Sony Corp., a Blu-ray backer. Now Toshiba is working with NEC to establish a DVD-friendly format as the next-generation choice.

The Toshiba-NEC proposal uses a blue laser, but other aspects of the system are kept the same as in current DVD systems. As for DVDs, the numerical aperture of the lens is 0.65 and the disk consists of two 0.6-mm platters bonded back-to-back.

The Blu-ray format, by contrast, has no compatibility with current DVD systems, and whether a particular Blu-ray disk system can play and record standard DVD disks is left to each company's product design decision.

The Toshiba-NEC proposed format includes both rewritable and read-only disks, whereas the Blu-ray format has not yet defined read-only disks. "As our proposal defines both ROM and RAM disks from the beginning, such incompatibility [of ROM drives not being able to read RAM disks] won't occur," said Hiroshi Inada, senior manager of NEC's functional-devices research laboratories. "Even if the dual-layer, 40-Gbyte writable-disk format is added later, ROM drives will be able to read the disk as well."

Disk capacity is 15 Gbytes for a single-sided, single-layer disk and 30 Gbytes for a single-sided dual-layer disk. The rewritable disk will have a larger capacity of 20 Gbytes for a single-sided, single-layer disk. Toshiba and NEC intend to add a 40-Gbyte single-sided, dual-layer rewritable disk to the proposal soon. With efficient bit rate control and compression, the 30-Gbyte disk can record about three hours of high-definition program material.

Compatibility concerns

Toshiba and NEC stressed the importance of DVD compatibility. "The industry has leaned toward 0.1-mm cover-layer disk technology" as the next step in optical disks, said Inada. "We also have been developing technology that uses a disk with a 0.1-mm cover layer as well. But a smooth transition from the current system to the next generation was more important, especially for disk systems used with PCs." So the challenge before the partners, he said, was "to realize large capacity based on the 0.6-mm-substrate disk that is used for DVD."

Toshiba and NEC had respectively been conducting research into next-generation systems based on a 0.6-mm disk substrate. The two merged their technologies after the Blu-ray Disc announcement to jointly propose a single, unified format to the DVD Forum.

Sticking to DVD specifications puts the proposed format at a capacity disadvantage compared with Blu-ray Disc systems, which boast a maximum of 27 Gbytes for a single-layer, single-sided disk. "Though disadvantageous in capacity, the proposed format is advantageous in other aspects," said Inada. Like current DVDs, the disks won't need a cartridge, making it possible to integrate slim drives into portable equipment. Dual-layer disks are much easier to produce than 0.1-mm cover-layer disks. That's because the back-to-back bonding of 0.6-mm-thick disks is widely done for current DVDs. Since the numerical aperture is 0.65, the same as DVD's, the pickup structure will be simple. An infrared, a red and a blue laser can share the same lens, easily providing backward compatibility.

"Our proposal is a draft. Taking consideration of other proposals, if any, we hope to boil down the final format within this fiscal year [ending next March]," said Inada.

The Blu-ray Disc founders — Hitachi, LG Electronics, Matsushita, Pioneer, Philips, Samsung, Sharp, Sony and Thomson Multimedia — opened the information on the Blu-ray Disc specifications in June and planned to begin licensing at the end of that month. But licensing has not started yet, the Sony spokesman said, because the backers have not hammered out whether it should be in the form of one-stop shopping or some other model.

None of the proponents have made clear just what their marketing plans are for Blu-ray Disk systems. Sony, however, is expected to introduce the first product sometime next year.