A computer disc about the size of a DVD that can hold 60 times more data will go on sale in 2006, according to its American developer InPhase Technologies, a Lucent spin off.

The discs, holding 300GB each, use so-called Tapestry holographic memory technology to store data by interference of light. They are also able to read and write data at 10 times the speed of a normal DVD.

InPhase Technologies has formed an alliance with Hitachi/Maxell to market and sell the discs. The first public demonstration was held at the International Broadcast Equipment Exhibition last week in Tokyo.

Tapestry can store more than 26 hours of broadcast-quality high-definition video on a single 300GB disk, recorded at a data rate of 160Mbps. The discs are 13cm in diameter and a little wider and thicker than conventional DVDs.

Normal DVDs record data by measuring microscopic ridges on the surface of a spinning disc. Two competing successors to the DVD format - Blu-ray and HD-DVD - use the same technique, but exploit shorter wavelengths of light to cram more information onto the surface.

The Tapestry system uses light from a single laser split into two beams: the signal beam and the reference beam. The hologram is formed where these two beams intersect in the recording medium.

The process for encoding data onto the signal beam is accomplished by a device called a spatial light modulator, which translates the electronic data of 0s and 1s into an optical 'checkerboard' pattern of light and dark pixels. The data is arranged in an array or 'page' of around a million bits.

At the point of intersection of the reference beam and the signal beam, the hologram is recorded in the light sensitive storage medium. A chemical reaction occurs in the medium when the bright elements of the signal beam intersect the reference beam, causing the hologram.

By varying the reference beam angle, wavelength or media position many different holograms can be recorded in the same volume of material.

as long as 1 disk doesn't cost as much as a 300gig hd,I'm in

Holographic storage developer InPhase Technologies has said it will announce its Tapestry hologram storage product in May. A version of the product was demonstrated at the NAB2008 show in Las Vegas earlier this month.

The bare facts are these: Tapestry consists of 120mm (5.25-inch) diameter clear plastic disks in a cartridge case. Holographic images are stored in the depth of the recording medium on the disk's surface using a blue laser.

The first disks are said to have a 50-year life and will perform reads and writes at 20MB/sec in a Tapestry drive which appears to be priced at $18,000. The disks will cost $180 each in volume and store up to 300GB.

"Subsequent generations of WORM devices will increase capacity to 800GB and transfer rate to 80MB/sec and then to 1.6TB and 120MB/sec," InPhase says on its web site.

It has taken 8 years for InPhase to develop its products with virtually all the functions of the technology requiring custom development. In this respect, InPhase has similarities with Plasmon, which has also developed its blue-violet laser UDO optical disks on its own.

A quick set of comparisons and contrasts looks like this:

LTO3 is four times faster than Tapestry and holds 100GB more but tape is not guaranteed to hold data for 50 years and needs its contents re-written to fresh media every so often. It is also not a random access medium, somewhat negating its faster I/O.

Blu-ray optical disks hold 25GB or 50GB and so have an immediate capacity disadvantage. They are, of course, cheaper but they are not promoted as having a 50-year life. That may change.

Plasmon's UDO has a capacity disadvantage, holding 60GB in its generation 2 version with UDO-3 set at 120GB and UDO-4 at 240GB on the roadmap. It does have a 50-year life but UDO-2 has a slower 12MB/sec I/O rate. UDO is also in use and not a version 1 product.

It would seem that InPhase will have the high-capacity, 50-year archive store market pretty much to itself for a few years.