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CD-RW ABCs

CD-RW Drive (CD ReWritable) / CD-E (CD-Erasable) Drive was first introduced in mid 1997 and is a popular alternative to the CD-R drive. CD-RW has the capability of being written to at least one thousand times.

Unlike the CD-R technology which uses a photosensitive dye, CD-RW disks uses an active layer of Ag-In-Sb-Te (silver-indium-antimony-tellurium) alloy that, in its original state, has a polycrystalline structure that makes it reflective.
When the CD-RW drive writes to the disk, the laser uses its highest power setting known as Pwrite. At this temperature which is usually between 500 and 700 degrees Celsius, the chemical structure will liquefy. In its liquid state, the molecules of the active material flow freely, losing their polycrystalline structure and taking on an amorphous state. When the material solidifies in this amorphous state, it loses its reflectivity. By selectively firing the laser, the drive leaves parts of the disc in its polycrystalline state, forming the lands, and parts in the amorphous state forming the pits.
To reverse the phase of a specific area on a disc, the laser operates at a lower power setting and heats the active material to approximately 200 degrees Celsius reverting it back from its amorphous to its polycrystalline state and then becomes reflective again.

The drawback with CD-RW discs is with the lower reflectivity of the disc itself can limit the readability. Originally in the 1980s, the CD standards specified that on a compact disc the lands should have a minimum of 70% and the pits should have a reflectance of 28%. However, on a CD-RW disk, the reflectance of a land is approximately 15% to 25%. Which with certain CD-RWs disks can cause certain CD-ROMs to not read the disks properly.

CD-R - (CD Recordable) Drive which you are able to write to once. Once the drive is written to, it cannot be erased.
CD-ROM -(Compact Disk Read Only Memory) The standard type of CD-ROM drive which is now shipped and found in the majority of computers today.
DVD - (Digital Versatile Disc) New standard released in 1995 which originally was called Digital Video Disc and later changed to Digital Versatile Disc. DVD offers an initial storage capacity of 4.7GB (of digital information on a single-sided, single-layer disc the same diameter and thickness of a current CD-ROM
DVD-RAM - ReWritable drive type that uses a phase-change technology like the CD-RW drives. However, DVD-RAM discs cannot be read by standard DVD-ROM drives because of the differences in both reflectivity of the medium and the data format.