Programmable read-only memory
A programmable read-only memory
) is a memory that comes blank, the contents of each bit is determined by a fuse or antifuse. The memory can be programmed once after manufacturing by "blowing" the fuses, which is an irreversible process. Blowing a fuse opens a connection while blowing an antifuse closes a connection (hence the name). Programming is done by applying high-voltage pulses which are not encountered during normal operation (typically 12 to 21 volts). Read-only
means that, unlike the case with conventional memory, the programming cannot be changed (at least not by the end user).
A typical PROM comes with all bits reading as 1, burning a fuse during programming causes its bit to read as 0.
Such PROMs are used to store programs permanently. They are frequently seen in computer games, or such products as electronic dictionaries, where PROMs for different languages can be substituted.
See also Erasable programmable read-only memory, or EPROM.