Companies are demonstrating new high-capacity DVD discs at Japan's giant computer show, CEATEC, this week.

Dual-layer versions of both competing DVD media – DVD-R and DVD+R – are on view, offering capacities (8.5GB) almost double those available today (4.7GB).

Pioneer, Koninklijke Philips Electronics and Mitsubishi (owner of the Verbatim brand) have all said they have developed prototype discs that can accommodate this amount of data.

Anticipating the need to store more data, the developers of the DVD format specified several additional types of disc when the format was decided on in the mid-nineties.

The simplest of these disc types, and the most common today, is the 4.7GB single-sided, single-layer disc – that is, a single recording layer that can be used on only one side.

Double-sided disc support

Developers also included support for double-sided discs, double-layer discs, and a combination of the two. Mitsubishi is already selling double-sided, single-layer discs that double the data capacity to 9.4GB by allowing recording on both sides of the disc. These require users to eject, flip-over and reinsert the disc when switching from side one to side two.

The prototype discs from Pioneer, Philips and Mitsubishi have a single recording side, like current discs, but two recording layers. By adjusting the focus of the laser beam, each layer can be targeted without disrupting data on the other. This allows for up to 8.5GB of data to be stored on a single-sided disc, which isn't quite the data capacity of a double-sided disc, but can all be accessed without the hassle of turning the disc over.

Dual-layer discs are already supported under the DVD-Video format and some commercial video discs already use the format. If you've seen a momentary pause in the middle of a DVD movie, it’s likely that the player is switching from layer one to layer two.

Pioneer, which developed the DVD-R prototype, still has some work to do on the technology and will propose it as a standard to the DVD Forum when its development is complete, it said. Philips, which produced the DVD+R prototype with Mitsubishi, said its disc should be ready for commercial launch next year.

Compatibility with existing drives and players might be an issue. Pioneer said its disc can be played back on most existing DVD players while Philips said ensuring compatibility with existing players was one of its prime concerns when developing the DVD+R disc. Both companies noted users will need to purchase new drives if they want to write to the new discs and Philips said drives are expected with the discs in 2004.

CEATEC takes place from October 7 to 11.