The DVD Forum has approved a standard for next-generation rewritable DVD discs with four times the current capacity.

The rewritable HD-DVD (High Definition and High Density-DVD) format was approved as the DVD Forum kicked off its general meeting in Tokyo this week. It specifies a 12-centimetre optical disc that can store up to 20GB of data on a single-sided disc compared to 4.7GB on existing DVDs. The format has been largely developed by Toshiba and NEC and a read-only version of HD-DVD, which can hold 15GB of data, was approved late last year.

The move ups the ante in the upcoming DVD format battle for futrure iterations of the technology. The four-way match currently features the Blu-Ray Disc, Sony's two Professional Disc formats; and Plasmon's Ultra Density Optical disc

While all four formats are physically incompatible, they all deliver a large jump in data storage because of the same blue laser technology. Blue light has a shorter wavelength than the red light used in CD and DVD systems and so the laser beam makes a smaller spot on the disc surface. That means each bit of data takes up less space on the disc and so more data can be stored on a disc.

The current meeting, which ends today, also saw the expansion of the DVD Forum's steering committee to 20 members with the addition of Microsoft and a unit of The Walt Disney Co.

The full member list is: Hitachi, IBM, Industrial Technology Research Institute (Taiwan), Intel, LG Electronics, Matsushita Electric Industrial Co. Ltd. (Panasonic), Microsoft, Mitsubishi Electric, NEC, Pioneer, Koninklijke Philips Electronics NV, Samsung Electronics, Sanyo Electric, Sharp, Sony, Thomson, Time Warner, Toshiba, JVC and Walt Disney Pictures and Television.