CDs, BDs, and DVDs come in several varieties.  Please describe "ROM," "R," and "RW" versions of these types of media.

What will be an ideal response?

• Read-only (ROM) versions of CDs, DVDs, and BDs contain permanent data stored on the disc during the manufacturing process. Data on CD-ROMs, for example, cannot be changed or deleted. These discs are typically used to distribute software and movies.
• Recordable (R) discs contain a layer of color dye sandwiched beneath the clear plastic disc surfaces. A writable drive can store data on CD-R, DVD-R, and BD-R discs by changing the dye color. The change in the dye is permanent, so data cannot be changed after it has been recorded.
• Rewritable (RW or RE) discs contain a crystal structure on the disc surface. The crystal structure of CD-RW, DVD-RW, CD+RW, DVD+RW, and BD-RE discs can be changed many times, making it possible to record and modify data much like on a hard disk.