Optical Tape Optical tape is made by ICI and packaged in a cassette for use as a WORM format data storage tape. Kodak are about to launch a competing system. Because the tape is a sequential carrier, the access time can be quite long. A laser beam in the write mode can change single spots to either an amorphous or a crystalline state so that, again, a digital bit stream is created. Dust and dirt of all kinds.
Humidity is, as with other data carriers, a most dangerous factor.
In the case of optical media it has a hydrolytic action on components such as the protection layer of CDs and a corrosive influence on all metal components including metallic reflective layers. More importantly, it is responsible for dimensional changes which may be of concern, especially in the case of multi-layer media. Mechanical integrity is of utmost, and underrated, importance. Even microscopic scratches can hinder the reading laser beam, as do fingerprints and other foreign matter. Mechanical bending of discs cause microscopic cracks which again divert the laser.