Like regular Compact Discs and CD-Rs, CD-RWs are composed of a polycarbonate plastic substrate, a thin reflective metal coating, and a protective outer coating. In a CD-RW, the reflective layer is an alloy that can change back and forth from a crystalline form when exposed to the laser, through a technology called optical phase change. The patterns created are less distinct than those of other CD formats, requiring a more sensitive device for playback. Due to this, CD-RWs cannot be read in some CD-ROM drives built prior to 1997. CD-ROM drives that can read CD-RWs will be designated as MultiRead to show compatibility.
Older CD-RW drives often cannot handle newer, high speed CD-RW discs. CD-RW media rated at over 4x speed carry a ‘high-speed’ logo.
12 cm CD-RW discs (8cm Mini CD-RW are also available) usually hold 74 minutes (650 MB) of data, although some can hold up to 80 minutes (700 MB) and, according to some reports, can be rewritten as many as 1000 times. With packet writing software and a compatible CD-RW drive, it’s possible to save data to a CD-RW in the same way as a floppy disk. CD recorders (usually referred to as CD burners), were once much too expensive for the home user, but now are similar in price to CD-ROM drives.