In a move that could influence the outcome of the rewritable DVD format battle, software giant Microsoft is joining the DVD+RW Alliance, the group that promotes and develops the DVD+RW format.

Microsoft will become the ninth member of the Alliance's policy-setting team, which also includes Philips Electronics, Hewlett Packard, Sony, Dell and Ricoh.

Although Microsoft will support other formats in its operating system, the software maker has now made it clear that DVD+RW is the format it prefers, said Hans Driessen, a spokesman for Philips and the DVD+RW Alliance.

"Microsoft will actively promote DVD+RW and invest in the development of the format," Driessen confirmed.

Rivalling DVD+RW are the DVD-RW and DVD-RAM formats, supported by the DVD Forum. DVD-RW is being pushed by Pioneer, while Hitachi, Toshiba and Matsushita are in the DVD-RAM camp.

The DVD+RW Alliance claims its format is the better one because DVDs created on a PC can be played back on most DVD players and DVD-ROM drives in PCs. This is not possible with DVD-RAM, which uses a disc in a cartridge. DVD-RW offers compatibility only when discs are created using a special recording mode, limiting edit capabilities, Driessen said.

In separate battle for the traditional DVD market, Blu-ray and AOD (advanced optical disc) are currently the two formats competing to replace existing DVDs.

Such conflicting technologies have been criticised in the past for confusing customers and creating the possibility of redundant hardware when one technology becomes more popular.