Rewriteable compact disk

CD-ROM not erasablenot rewritable technology identical with audio compact disk (CD-DA) substrate and information layer from polycarbonate (PC)... 

The palladium phthalocyanine (67), developed by Mitsui Toatsu and Ciba58,59 is one of the leading phthalocyanine infrared absorbers for CD-R (Compact Disk-Rewritable) (see Chapter 9.13). Bulky groups (R) reduce undesirable molecular aggregation, which lowers the extinction coefficient and hence the absorptivity and reflectivity. Partial bromination allows fine tuning of the film absorbance and improves reflectivity. The palladium atom influences the position of the absorption band, the photostability and the efficiency of the radiationless transition from the excited state.58 It is marketed by Ciba as Supergreen.60... 

The top layer is translucent and the bottom layer opaque. Data can be read from either k layer by refocusing the laser. In addition DVDs maybe double-sided. DVD formats also have a more efficient error-correction system. The potential capacity of a doublesided double-layer DVD is up to 17 gigabytes. DVDs have been increasingly used in computing as a higher-capacity version of compact disks. As with compact disks, there are various types. DVD-ROM (DVD readonly memory) is similar to CD-ROM. DVD-R (DVD-recordable) is similar to CD-R. There are also different rewritable formats DVD-RAM, DVD+RW, and DVD-RW. 

Compact disk erasable/compact disk recordable (CD-E/CD-R) These define the writable versions of the compact disk. CD-E is a rewritable media and CD-R is a write-once media. 

---