Read-Only Memory (ROM)
is a type of non-volatile memory used in computers and other electronic devices . data store in ROM can only be modified slowly, with difficulty, or not at all, so it is mainly used to store firmware (software that is closely tied to specific hardware and un likely to need frequent updates).
Strictly, read-only memory refers to memory that is hard-wired, such as diode matrix and the later mask ROM (MROM) . although discrete ciruits can be altered in principle, integrated circuits (ICs) cannot and are useless if the data is bad or requires an update . that such memory can never be changed is a disadvantage in some applications . more recently, ROM has come to mean memory that is read-only in normal operation, but a technician using special equipment can erase or reprogram to updating firmware or to correct an error
Other types of read-only memory, in the newer sense of the term, include erasable programmable read-only memory (EPROM) and electrically erasable programmable read-only memory (EEPROM) . these types of memory can be erased and re-programmed mulitple times, but only by using equipment and processes unavailable to typical and user .