Big digital disk debuts

FMD might one day replace both DVD and CD

By BBC News Online internet reporter Mark Ward

Digital disks are set for a big boost in capacity.

By the end of the year, US firm Constellation 3D claims that it will be selling a new generation disk it hopes will replace existing DVDs

Initially the new disks will have 10 times the capacity of a DVD, and by the middle of next year, the company says it will be making disks with 20 times more storage room.

Constellation claims that existing DVD drives will be able to read its disks after only a slight modification.

The company says it can squeeze a lot more data on to a disk because it has found a way to record information on multiple layers within the disk.

Every layer holds the equivalent of an existing DVD - around five gigabytes of data.

Currently, Constellation has made disks with 10 layers but expects that as the technology improves it will be able to make 100-layer disks.

Groovy space

On a DVD, information is encoded in the form of a series of pits and spaces, called "lands", in a groove spiralling out from the centre of the disc.

A laser reads the sequence of different length pits and lands, and this is converted into a stream of digital information.

DVDs use more powerful red lasers than those in a CD player. This means that the pits and spaces can be smaller and more information can be crammed on to the disk.

By contrast, the new Constellation disks overlay the pits and lands with a fluorescent material which emits light when struck by the laser.

This incoherent light has a slightly different wavelength to that of the laser beam and can travel through the layers of the disk undisturbed.

"The fluorescent compounds can be tailored to have different properties," said Patrick Maloney, senior vice president at Constellation 3D. "They can be made to play once or you can make it last 150 years."

Moving pictures

The new disks will take time to reach consumers, however. The first users are likely to be film studios in need of storage media with enormous capacities.

Some cinema goers saw a digital version of Toy Story 2 © Disney/Pixar

Mr Maloney said Constellation was initially talking to film studios such as Lucasfilm and Disney who are starting to make digital versions of films that are stored like any other computer file.

Last year, some cinema-goers who went to see Toy Story 2 saw a digital version rather than one printed on film.

Eventually, Constellation expects computer makers to bring out machines with hybrid drives that can read CDs, DVDs and its own disks.