CD-R and CD-RW
CD-R is the term used to denote CD-Recordable media. CD-R discs are recorded permanently. Once information is written, it cannot be erased. Data can be added until the disc is full. CD-R is good for creating archived information that need not be changed, or for distribution, because the price of CD-R media has dropped rapidly in the last few years.
CD-RW is the term used to denote CD-ReWritable media. CD-RW discs can be written to many times. CD-RW media is rated for one thousand different writes to the media. CD-RW is perfect for personal file storage or for creating reliable backups that can be added to as necessary, and even rewritten as your backup scheme requires.
While CD-RW media is more expensive than CD-R media it has a lower cost per megabyte than other competing technologies, such as Magneto–Optical or even magnetic removable media drives.
CD-RW drives are very versatile for transporting information to both older and newer CD-ROM and DVD-ROM drives. CD-RW media can be read by newer CD-ROM and DVD-ROM drives. These newer drives are known as Multi-Read (MR) drives. And even though CD-RW media cannot be read by older CD-ROM drives, the Sony CD-RW Recorder can write to CD-R media which can be read by standard CD-ROM drives and Audio CD Players.
How CD-R and CD-RW work
CD-ROM drives (CD-R and CD-RW drives as well) read the one and zero bits by difference in reflectivity. Mass produced Compact Discs are created by stamping “pits” in the CD. These “pits” reflect differently than the “land” which is the area between “pits.”
CD-R drives work by using a laser beam to heat the recording layer, causing a chemical reaction in that spot so CD-ROM players will see this as a “pit” and the unburnt area as “land.”
CD-RW uses what is known as a “Phase Change” technology. In the CD-RW media is a substance which can be changed from an amorphous “mark,” that very closely resembles the pits of a stamped CD, to a crystalline state which resembles “land.” The laser beam of the Sony CD-RW Recorder Drive changes the crystalline state to the amorphous state by use of a laser to quickly heat the spot on the disc, forming a mark. To change the amorphous state back to the crystalline state, the laser beam uses a lower power setting to transition the mark back to the crystalline “land.”
Performance
The CD-RW Recorder drive is capable of writing CD-R discs at 8X speed and CD-RW discs at 4X (quad) speed. Quad speed or 4X means that the drive can write (also called record or burn) a CD-RW disc at 600 kilobytes per second. This rate allows the drive to record a full 650 megabyte CD-RW disc in about 18 minutes. At 8X speed the drive can write at 1200 kilobytes per second, or record a full 650 megabyte CD-R disc in only 9 minutes.
