Pronounced EE-prom (almost rhymes with eon), this is an acronym for Erasable Programmable Read Only Memory. Various types of ROM (Read Only Memory) chips are used in many computers and synthesizers to hold instructions or other data (such as sound data) that the machine uses. ROM chips must be permanently programmed at the time of manufacture. While being relatively inexpensive, this can be a problem because all decisions about the data must be permanently decided at a relatively early stage in the design of the product. PROM or Programmable Read Only Memory has the ability to be programmed at any time. The only caveat being that once programmed, the data is permanent. EPROM chips can be erased by subjecting them to ultra violet light radiation. This means they can be reprogrammed and reused as needed, hence the name EPROM.