Nine of the world's largest electronics companies have taken a joint step towards commercialisation of a next-generation optical disc system and with it raised the possibility of a new format battle.

The companies have agreed upon basic specifications for a blue laser-based optical-disc system, named 'Blu-ray disc', and plan to have the first version of the specification finalised and ready for licensing within the next few months.

The format is being aimed initially at recording of high-definition television video — an application in which more than 10GB of storage space is eaten up with just one hour of video — but for the industry as a whole marks a milestone in the road towards systems offering even more data storage than DVD (digital versatile disc).

Blu-ray discs will be rewritable, 12cm discs and have a data capacity of around 27GB, which is enough for two hours of high-definition digital television. They will employ blue lasers, rather than red lasers which are used in DVD and CD players.

Blue lasers have a shorter wavelength — 405nm (nanometres) compared to around 650nm on DVD systems — and that means the laserbeam can be focused on to a smaller area of the disc surface. In turn, this means less real estate is needed to store one bit of data and so more data can be stored on a disc.

Prototype blue laser-based optical-disc systems have been around for more than a year. However, one problem has hampered development of commercial systems: cost. A sample blue-laser diode currently costs around $1,000, making consumer products based on the parts unrealistic. However, Nichia, the major source for blue lasers, is expected to begin commercial production this year and the price of a blue-laser diode is expected to tumble once the company begins turning them out in volume.

Expecting the price to begin falling soon, many electronics companies have recently taken the lid off blue laser-based development systems and the similarity of the work being done sparked the nine companies to begin working together, they said today.

Among the Blu-ray disc group are six of the 10 companies that worked on developing the DVD format: Hitachi, Matsushita Electric (Panasonic), Philips, Pioneer, Sony and Thomson Multimedia. They have been joined by Sharp, LG and Samsung.

Four of DVD's main backers — Mitsubishi, AOL Time Warner, JVC and Toshiba — are absent from the initial Blu-ray disc consortium.

Toshiba's absence is the most significant. The company is chair of the DVD Forum, the industry group that promotes DVD and handles development of new DVD formats, and has publicly stated that it intends to propose its prototype blue laser optical-disc format to the organisation as a next-generation DVD format. It's absence from the Blu-ray disc group raises the possibility that a format battle, just like the one that took place before the industry settled on DVD, may be about to begin again.

"We are not in that discussion group," said Midori Suzuki, a spokeswoman for Toshiba. "For the next-generation blue laser optical disc, we will keep proposing a standard to the DVD Forum."

Before the DVD specification was announced, a group led by Toshiba and Matsushita was pushing a system called Super Density while Sony and Philips were promoting their Multimedia Compact disc. In the end, both sides came together to back one format, although in the computer area, where multiple standards often battle against each other or coexist, there has not been such harmony.

The DVD Forum has standardised two rewritable formats, DVD-RW and DVD-RAM, but a group of companies including forum members Sony and Philips have developed their own competing system, DVD+RW, which despite its name is not an official DVD format. The latter two companies are also pushing Double Density CD, which is a CD-based technology with double the storage capacity of regular CDs, and a multitude of other formats also exists, including MO (magneto optical) and CD-RW.

As if to demonstrate the concessions that had to be made to get the nine companies together around a single format, the Blu-ray disc group announced discs are expected to be available in three similar sizes: 23.3, 25 and 27GB.

The reason for offering discs in three similar capacities? Some companies want to keep the price of discs low and so propose using cheaper materials that will be able to hold slightly less data while other companies prefer selling more expensive discs that can hold more data, the group said.

The companies are also yet to decide on whether the discs will be enclosed within a cartridge or not and today displayed prototype discs (pictured) with and without protective cartridges.

Right now much of the talk about blue laser-based systems is focused around high-definition television, where data needs are great. However the Blu-ray disc group is also considering development of write-once and read-only (ROM) formats for use with personal computers, the group said.