Mask ROM

Mask ROM (MROM) is a type of read-only memory (ROM) whose contents are programmed by the integrated circuit manufacturer (rather than by the user). The terminology mask comes from integrated circuit fabrication, where regions of the chip are masked off during the process of photolithography. Mask ROM (MROM) is a type of read-only memory (ROM) whose contents are programmed by the integrated circuit manufacturer (rather than by the user). The terminology mask comes from integrated circuit fabrication, where regions of the chip are masked off during the process of photolithography. It is common practice to use rewritable non-volatile memory – such as UV-EPROM or EEPROM – for the development phase of a project, and to switch to mask ROM when the code has been finalized. For example, Atmel microcontrollers come in both EEPROM and mask ROM formats. The main advantage of mask ROM is its cost. Per bit, mask ROM is more compact than any other kind of semiconductor memory. Since the cost of an integrated circuit strongly depends on its size, mask ROM is significantly cheaper than any other kind of semiconductor memory.