Acronym for read-only memory. A nonvolatile semiconductor memory device used for the storage of data that will never require modification: the memory contents are permanently built into the device during its manufacture according to a specially created pattern or mask. It is thus sometimes called mask ROM to distinguish it from programmable ROM, i.e. PROM. Although it is possible only to read data from the memory locations of a ROM, the locations can be accessed in any order with equal speed. Hence there is random access to any of the locations in ROM. See also EAROM, EEROM. Compare RAM.