DVD discs capable of story 15GB - three times more than existing DVDs - will be available at the start of next year, according to Toshiba.

The write-once HD-DVD-R discs will however faced competition at the same time from the alternative HD-DVD-RW format, which is expected to be able to store 20GB, will be rewriteable but also cost significantly more.

HD-DVD's backers had already discussed the development of the HD-DVD-RW discs, but had not talked about a write-once technology until this week.

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 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 yesterday.

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.

Toshiba plans to sell both HD-DVD recorders and PC drives compatible with the HD-DVD-R discs in Japan and the US early next year. Sanyo plans to launch a recorder in 2006.

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.