CD-RW (Compact Disk – Rewritable): CD-RWs are compact disks where data can be rewritten multiple times. The same concept of a CD-R is used, just that instead of a dye an alloy of silver, indium, antimony, and tellurium is used. In CD-RW, lasers with different powers are used. When a high power laser is used, the alloy melts and the crystalline state is converted to the amorphous state. When a medium power laser is used, the crystalline state is unchanged. When the CD-RW is played the crystalline and the amorphous spots are recognized.
DVD (Digital Video / Versatile Disk): DVD is a type of optical disk which is used for storage. It looks like a CD-ROM but provides more storage space. Here’s how a DVD is made: Holes of diameter 0.4 micrometer are made in a coated glass disk by using an infrared laser. This glass disk is used to make a mold and molten poly-carbonate resin is injected in to the holes. After that a thin layer of reflective aluminum is deposited on the poly-carbonate. It is then topped by a semi reflective layer.