Another form of non-volatile random access storage is the read-only memory (ROM). Here a single memory bit is nothing more than a connection that is either open or closed. The most common ROM types are known as field-programmable (as opposed to factory programmable). This programming process consists of stepping through all the bits and setting the necessary ones by burning open the fuse-like material associated with that bit.
There are many varieties of field-programmable ROM units:
PROM) - electrically erasable PROMs.
The most common uses of ROM memory in a computer are to provide initialization such as memory tests and disk bootstrapping.