DVD formats at a glance

DVD RAM

The second version of DVD-RAM, which has been ratified by the DVD Forum, has a capacity of 4.7Gbytes. This format, supported by Panasonic, is at a disadvantage as double sided discs come in sealed cartridges. Single sided discs can come in open cartridges, but can only be written while in the cartridge.

DVD + RW

This is backed mainly by Sony but also has the support of Philips and Hewlett-Packard. It has not been ratified by the DVD Forum, and is effectively a direct competitor to DVD RAM. Reflectivity differences, among other problems, mean that the disc can't be read by read by DVD-Video players. It has a capacity of 2.8Gbytes, with upgrade to 4.7Gbytes by 2001 expected.

DVD-RW

Developed by Pioneer, this phase-change format is based on DVD-R and can be rewritten around 1000 times. Pioneer plan to make the format compatible for playback with DVD-Video. It offers up to six hours of recording time and has a 4.7Gbyte capacity. It uses groove recording with the address information on land areas for synchronisation at write time.

DVD R

A write-once standard with limited applications, unlikely to be economic for end users. Useful for organisations which do a lot of archiving or need to store huge amounts of data that won't need to be altered. Possibly useful for games developers. Currently drives are prohibitively expensive at around £5000. Like CD-R, the format uses organic dye polymer. Capacity is 4.7Gbytes.