Types of Recordable Optical Disc
There are numerous formats of recordable optical direct to disk on the market, all of which are based on using a laser to change the reflectivity of the digital recording medium in order to duplicate the effects of the pits and lands created when a commercial optical disc is pressed. Emerging technologies such as holographic data storage and 3D optical data storage aim to use entirely different data storage methods, but these products are in development and are not yet widely available.
The earliest form is magneto-optical, which uses a magnetic field in combination with a laser to write to the medium. Though not widely used in consumer equipment, the original NeXT cube used MO media as its standard storage device, and consumer MO technology is available in the form of Sony's MiniDisc. This form of medium is rewriteable.
The most common form of recordable optical media is write-once organic dye technology, popularized in the form of the CD-R and still used for higher-capacity media such as DVD-R. This uses the laser alone to scorch a transparent organic dye (usually cyanine, phthalocyanine, or azo compound-based) to create "pits" (i.e. dark spots) over a reflective spiral groove. Most such media are designated with an R (recordable) suffix. Such discs are often quite colorful, generally coming in shades of blue or pale yellow or green.
Rewritable, non-magnetic optical media are possible using phase change alloys, which are converted between crystalline and amorphous states (with different reflectivity) using the heat from the drive laser. Such media must be played in specially tuned drives, since the phase-change material has less of a contrast in reflectivity than dye-based media; while most modern drives support such media, many older CD drives cannot recognize the narrower threshold and cannot read such discs. Phase-change discs are designated with RW (ReWriteable) or RE (Recordable-Erasable). Phase-change discs often appear dark grey.
A new technology has emerged whereby physical changes to a long-lived media creates a new "write-once" option. A drive offered by Millenniata is supposed to record data on proprietary media with a data life-time said to be "forever".
Read more about this topic: Optical Disc Recording Technologies
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