Mask ROM

Mask ROM refers to a kind of ROM (read-only memory) whose contents are programmed by the IC manufacturer (rather than by the user). The terminology mask is used in IC fabrication.

It is common practice to use rewritable UV-EPROM for the development phase of a project, and to switch to mask ROM when the code has been finalized.

The main advantage of mask ROM is its cost, since it is significantly cheaper than other kinds of ROM, but if an error in the data or code is found, the mask ROM is useless and must be replaced in order to change the code or data.