PROM is not an example of an optical disk. Erasable Programmable Read Only Memory (EPROM) is Programmable Read Only Memory (Programmable ROM) that can be erased and re-used. An optical disk is a flat, usually circular disk that encodes binary data in the form of pits and land on one of its flat surfaces. It is used for digital preservation, storing music, video on data and programs for personal computers. Blue ray disk, CDROM and DVD are the examples of an optical disk.