Acronym for programmable read-only memory. A form of semiconductor read-only memory, ROM, whose contents are added by a separate process after the device has been manufactured. This process of programming the PROM is accomplished by means of a device known as a PROM programmer. In general the programming process involves the destruction of fusible links within the PROM and is irreversible, i.e. the contents of the memory cannot be altered. Certain PROMs, including EPROMs, can however be reprogrammed numerous times. See also EEPROM, EAPROM.