CD Interoperability: Four different technologies use similar 4.5 inch optical media. There is some interoperability. CDROM, write once CD (CD-R) and rewritable CD (D-RW) use 785mm lasers at varying powers to read and, for CD-R and CD-RW, write their respective disks. All store 650mb. DVD uses 650nm lasers to read multilayer 4.7 GB media.

CDROM consists of a reflective layer in back of pits mechanically impressed into plastic. CD-R uses a reflective layer in back of a dye layer whose color can be irreversibly altered by a strong laser beam. CD-RW, uses a reflective layer in back of a solid material sandwiched between heat conductive layers. The solid material is melted and condenses into either amorphous or crystalline material depending on the strength of the laser beam.

The "contrast" level difference between the media is considerable -- with CDROM being the highest, CD-R next, and CD-RW the worst. Older CDROM drives usually can not read CD-R or CD-RW. 24X and higher CDROMs are manufactured to comply with the industry Multi-read specification and should read CD-R and CD-RW disks. In practice, the quality of the media, the age of the drive and the state of cleaning of the laser lens can affect readability. DVD drives can usually read CDROM and often can read some CD-R disks.

See PC Magazine Jan18,2000 p124 for more details

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