Magneto Optical Information

There is some ongoing controversy on the longevity of DVD-R and DVD-RW media. Some report DVD media will last for over a 100 years, while others report of media that are not readable even after a few months. To understand why both parties could be right, it is necessary to understand the technology behind optical media. CD-R and DVD-Recordable (whether plus or minus media) use a technology called Dye polymer. A layer containing a light-activated dye formulated from cyanine, phtalocyanine or azo is sandwiched between the reflective layer (aluminium or gold) and the protective outer layer of polycarbonate. When a high-powered laser is beamed on the disk, the dye becomes darker where the laser has hit the disk. The alternating bright and dark spots are read as the bit pattern that has been recorded.

Magneto optical disks make use of the Curie point. When heated to the Curie point, magnetic material immediately realigns its polarity to that of an adjacent magnet. In optical drives, the write heads heat the area being written with an intense laser beam while simultaneously exposing that same area to a magnetic field. This causes the exposed area to become a bit darker than the non-exposed areas, again making for a difference in reflectivity. When reading, the laser power is reduced so that the Curie point is not reached. This enables a Magneto Optical disk to be written about one million times.

First of all, Magneto Optical disks are certified to be far more reliable than CDR or DVD-R. The reason is that the technology has been tested thoroughly--high humidity paired to fluctuating temperatures ranging from minus 10 centigrade to 40 centigrade makes for pretty dependable ageing tests--and has been found to last for 30 years. That is: with data, recorded and all. Condition is that you store the media right. Magneto Optical must be stored out of sunlight, and in a normal humidity environment. Shelf life for Magneto Optical is well over 100 years. Storing them upright is a good idea so the disk cannot sag under its own weight, inside its plastic protective cover. If the disk sags, the head cant align with the areas on the disks surface properly anymore, and cant be read as a consequence.

Magneto Opticals, however, are pretty exotic archival media. They are often used by the healthcare industry, banks, insurance companies, and the government. But out of these industries Magneto Opticals are not often used as media. The drives are considerably expensive and the Magneto Optical itself seems deemed to disappear because most of the major vendors have stopped manufacturing drives for the media. Sony is about the only one who still makes drives, but even Sony has quietly stopped R&D on the next-generation Magneto Optical technology and has introduced Blu-ray.

Nevertheless, Magneto Optical is a superior archival format because it is insensitive to magnetic fields and has a long archival life. Because Magneto Optical is rather expensive, it doesn't matter much which brand you buy. Sony is a good brand, and so is Verbatim or Imation.

CD-R and DVD-R are an entirely different matter. Many cheap CDR and DVD-R disks (and this goes for RW media as well) are made in plants in the Far East where price is more important than quality. This results in disks that are faulty or are not properly coated or protected. If the disks dye surface is not properly protected by the polycarbonate layer, aluminium disks (the version that's commonly used in cheaper versions) tend to oxydate. There go your data...

More expensive disks are subjected to more thorough testing and better quality control. For example, Kodak uses the gold coating on its disks, while Verbatim DataLifePlus products use a Super AZO based dye with a silver reflection layer especially designed for longevity. Cheap CD-R and DVD-R dont last long and are certainly not the best media to trust your data to. But both Kodak and Verbatim have a very good track record for the quality and longevity of their media.

However, even with good quality, CD-R and DVD-R should be handled with care. Scratches and sweat from your hands may influence longevity in a negative way. Verbatim tests its media applying the Arhenius method to project life at office environments. Their testing reveals an archival life for their media of 100 years under the following conditions:

• No corrosive gas in the air
• No scratches or finger prints on the media surface
• Temperature control within 2 degrees centigrade of 25 degrees
• Humidity within 55% and a marging of 5RH%
• Media stored in jewel case
• Media not exposed to sunlight or UV light

This article has been based on data provided by Gartner Group and Verbatim.