The world's Big Nine electronics companies have swallowed corporate pride and agreed on a single standard and name - Blu-Ray - for the next generation video and computer optical disc. Although good for the consumer, they are putting the future of their fledgling recordable DVD systems in jeopardy.

Blu-Ray is backed by Hitachi, LG, Matsushita (Panasonic), Pioneer, Philips, Samsung, Sharp, Sony and Thomson. Only Toshiba, the main inventor of DVD, and JVC, which has a vested interest in VHS, are missing.

The new format will use a blue laser for recording and playback. A single-sided 12 centimetre Blu-Ray disc stores 27GB of computer data, records 13 hours of broadcast TV or holds 2 hours of High Definition video.

Prototypes already exist, and have been demonstrated by Philips, Sony and Panasonic. Licensing for manufacture begins within a couple of months and the first Blu-Ray recorders could go on sale next year.

Bad news

This could be very bad news for the three rival and incompatible recordable DVD systems, DVD-RAM (Panasonic), DVD-RW (Pioneer) and DVD+RW (Philips), which are just going on sale.

All use a red laser, with 650 nm wavelength, and can only store 4.7 GB on a single sided DVD. TV recording time is only one hour in best quality mode, and two, three or four hours with compromised pictures. Data capacity is inadequate for non-stop backup of a PC hard drive. The data transfer rate, around 10 Mbps, is not fast enough for high quality video.

A blue laser, with a 405 nm wavelength, can focus light more tightly into a smaller spot and so cram more data on a 12 centimetre disc. The data streams at 36 Mbps, which is fast enough for HDTV. As with recordable DVD, the recording is made in a phase change coating. Blu-Ray uses a very thin layer, 0.1 millimetres thick, to stop any tilt of the disc optically distorting the laser beam.

Everything is different

The 27 GB capacity will increase later to 50GB, thanks to dual layer discs, proposed by Panasonic.

The Blu-Ray group is still discussing whether the disc can be naked or must be housed in a protective cartridge.

Existing CD and DVD players and recorders will not be able to use Blu-Ray discs. New Blu-Ray players will need infra-red, red and blue lasers if they are also to play all kinds of CD and DVD recordings.

Speaking from the press launch in Tokyo, Chris Buma of Philips, says: "Except for the size of the disc, everything is different".