Erasable Optical Media Is Closer to Being Real

By Tyre, Terian | T H E Journal (Technological Horizons In Education), October 1988 | Go to article overview

Erasable Optical Media Is Closer to Being Real


Tyre, Terian, T H E Journal (Technological Horizons In Education)


Erasable Optical Media Is Closer to Being Real

Described by the manufacturer as a breakthrough in media, not hardware, Tandy Corp.'s THOR-CD technology makes it possible to write, erase and rewrite audio CD-compatible optical discs. THOR stands for Tandy High-intensity Optical Recording.

Educational institutions, which have extensive data storage needs but also require that any storage system be highly flexible and easily accessible, could well be one of the first beneficiaries of this technology.

The announcement of the new development in optical media precedes the introduction of any products by 18 to 24 months. This period is the normal manufacturing lead time to build player/recorders, according to Ed Juge, director of market planning for Tandy Corp. Several patents have been applied for by the firm.

How It Works

In general, current optical media uses microscopic "pits" and "lands," located in a substrate layer of the disc, to represent the basic units of binary code. To read the data, a low-power laser beam shines onto the disc, and various circuitry interprets the amount of light reflected back. A flat surface, or land, has much higher reflectivity than does a pit.

THOR-CD media utilizes both thermal and optic technologies. A laser creates pits in a heat-sensitive dye polymer material. These pits have the same form, fit and optical properties found in the pits of a standard audio CD or CD-ROM disc. The breakthrough is that the pits, while environmentally stable, can be removed by thermo-optically reversing the process. Thus the media is restored to its original form, allowing a disc to be erased and re-recorded over and over again.

According to a press release from Tandy, the erase process can be both bulk (erasing the entire disc at once) and spot (erasing just an individual pit). Discs may therefore be wiped totally clean for recording all new information. Or discs can be edited, with new data written only in specific locations.

Special Sauce

Dye polymers are not new to the optical media industry. A number of firms have been working with them for years for a variety of applications.

Optical Data, Inc. in Beaverton, Ore., has been researching the use of dye polymers with optical media for six years. Its technology involves a two-layer scheme, and the company was granted a U.S. patent on the process in January of this year.

Tandy has an option to acquire the license for Optical Data's technology, according to Bill Livermore, the marketing director for Optical Data. Tandy marketing information representative Lynn Handley says the Optical Data technology was utilized as a "guidepost" in developing THOR-CD. Tandy's unique contribution is a coating over the dye polymer. Code-named "special sauce" by Tandy engineers, the coating adds a reflective layer that provides the compatibility with current audio compact discs.

Question of Compatibility

The significance of the THOR technology, according to Tandy, is its complete compatibility with current audio CD and CD-ROM players. A THOR-recorded disc can be played in any audio CD or CD-ROM player.

Other write/erase/rewrite optical data disc systems do exist, but they use "bumps," not pits. This makes them incompatible with current compact disc hardware. By retaining pits, the THOR technology remains true to current audio CD standards.

The use of pits in THOR optical media also means that educators, administrators and students are provided with the same kind of access times, transfer rates and storage capabilities offered by current CD-ROM optical media and hardware.

THOR Timetable

According to Tandy, initial efforts will focus on developing and producing the blank media and an audio CD-compatible recorder. The recorder will play existing audio CDs in addition to playing, recording and erasing THOR media. …

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