Volume production of a write-once HD-DVD-R disc that can store 15G-bytes of data will begin in the first half of next year, about the same time that HD-DVD recorders and PC drives will become available, Toshiba and two optical disc makers said at a news conference.

The HD-DVD-R discs, which have about three times the storage capacity of today's DVD-R discs, should give consumers who want to record and store content on the HD-DVD format an alternative to the 20G-byte HD-DVD-RW discs that will also be in shops about the same time, according to Toshiba.

HD-DVD's backers had already discussed the development of the HD-DVD-RW discs, which can be rewritten many times, but had not talked about a write-once technology until very recently. The companies would not discuss pricing, but the write-once discs are expected to offer a cheaper alternative to rewritable discs for customers who buy HD-DVD equipment.

HD-DVD is competing with the Blu-ray Disc format to become the next-generation DVD technology. While Blu-ray backers Sony and Matsushita promote Blu-ray's high storage capacity as its main advantage for consumers, HD-DVD's chief virtue is that it can be made on the same equipment used to manufacture DVDs, according to Toshiba and NEC, the format's principal backers.

This reduces costs for manufacturers because they don't have to buy new manufacturing equipment, and means that HD-DVDs can be made for nearly the same price as DVDs, its backers claim.

However, that compatibility with DVD-making equipment hadn't extended to HD-DVD-R because of an issue with the layer of dye used to store data in write-once discs.The problem has now been overcome, Hideaki Ohsawa, a senior manager with Toshiba's Core Technology Center, said.

HD-DVDs have the same structure as DVDs, but in HD-DVDs, data is written with a blue laser that has a narrower wavelength than that of the red lasers used for DVDs. The narrower wavelength means more data can be stored, but the dye used in DVD-R discs isn't sensitive enough to work with blue lasers, Ohsawa said.

The trick has been to make dye that is more sensitive, can be spun onto discs with the same process used for DVD-R production, and is strong enough to withstand many replays. Other dyes developed to date have not met all those criteria, according to Toshifumi Kawano, a senior manager at disc maker Mitsubishi Kagaku Media Co.

But Mitsubishi Kagaku, working with disc maker Hitachi Maxelland dye maker Hayashibara Biochemical Laboratories, have now achieved that goal, he said.

Mitsubishi Kagaku has so far produced about 1,000 prototype discs, and Hitachi Maxell has also produced prototypes. Both companies are confident they can mass-produce HD-DVD-R discs with the same equipment they use to make DVD-R discs, he said.

Before the disc makers companies can gear up for production, the HD-DVD-R specification needs to be finalized by the DVD Forum, the standards body for the DVD format. This should be done within the next two months, according to Junko Furuta, a spokeswoman for Toshiba.

So far, only Mitsubishi Kagaku and Hitachi Maxell have said they'll make HD-DVD-R discs, but a number of disc makers who are members of the DVD-Forum are expected to announce production plans later, she said.

Toshiba plans to sell both HD-DVD recorders and PC drives compatible with the HD-DVD-R discs in Japan and the U.S. early next year, she said. Sanyoplans to launch a recorder in 2006, it said.

The first HD-DVD-R discs are single-layer discs that will only record at 1x speed. Both Mitsubishi Kagaku and Hitachi Maxell are already looking to improve the discs' recording speed, and both want to develop a higher-capacity version, they said. Because of various technical limitations with the discs themselves, 8x is the maximum recording speed that can be developed for HD-DVD-R discs, Kawano said.

"Making the 2x type and the 4x type is not so difficult, but making the 8x type will need a more powerful laser and it will take more time," he said.

The 2x version could be ready in about a year from now, Ohsawa said.

A dual-layer, 30G-byte disc could take several years to develop, Kawano said.