Plasmon has developed a new optical disc for compliance-based systems that allows selected data to be physically destroyed on the disc while leaving other data intact, the company said Monday.

The disc is based on Plasmon's UDO (Ultra Density Optical) optical media format and will be offered as a third media choice from Monday, the company said. The compliant write-once media will have a capacity of 30G bytes, the same as the write-once and rewritable versions of UDO, and will cost US$65 per disc.

That's halfway between the $60 and $70 the company charges for write-once and rewritable media respectively.

UDO is a phase-change optical storage system. In such systems, data is stored by changing the state of the disc's recording layer between amorphous and crystalline. Such changes affect the disc's reflectivity and it's this change that is detected when data needs to be read off the disc.

In the compliant write once discs data is selectively destroyed by changing the entire state of an area occupied by a file into the crystalline state.

"There is absolutely no trace of the original data," said Dave DuPont, a U.S.-based spokesman for U.K.-based Plasmon. "There is no way you can get the data that was there. This is in stark contrast to hard-disk drives where data is overwritten and it's still possible to get it back. We call our process data-shredding."

However, the system has been designed to leave the file's meta data untouched so that a record exists of what was there and makes it possible to verify what has been destroyed.

Plasmon started working on the system earlier this year after getting requests from customers for such a feature, DuPont said. The companies envisage the media as useful in two main scenarios.

The first, which DuPont said is more common in Europe than the U.S., is where organizations are required by privacy laws to destroy certain personal data after a specified period of time. The other, which is more of an issue for U.S.-based companies, involves disposal of data once it's no longer required to be kept by law.

"It's the elimination of the smoking gun," he said. "After the organization is no longer required to keep the data, if they keep it it can be used as evidence in legal proceedings."

UDO was launched in November 2003 and is based on a similar blue-laser technology to that used in the HD-DVD and Blu-ray Disc consumer optical media formats. UDO discs are encased in cartridges that are almost identical to Magneto Optical (MO) discs which means it's possible to mix and match MO and UDO drives in the same library.

Doing so allows companies with MO-based archive systems to gradually replace the older MO system. A second generation disc capable of storing 60G bytes is due on the market in late 2006, said DuPont.