Programmable read-only memory

A programmable read-only memory (PROM) is a memory that comes blank, usually with all bits reading as 1, and can be programmed by applying a high voltage (typically 12 to 21 volts) and writing to it. Each bit is a fuse, burning which causes it to read as 0.

Read-only means that, unlike the case with conventional memory, the programming cannot be changed (at least not by the end user).

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.