RAM computer memory available to the user for creating, loading, or running programs and for the temporary storage and manipulation of data, in which time of access to each item is independent of the storage sequence.
ROM computer memory in which program instructions, operating procedures, or other data are permanently stored, generally on electronic chips during manufacture, and that ordinarily cannot be changed by the user.
PROM a memory chip whose contents can be programmed by a user or manufacturer for a specific purpose.
EPROM a memory chip whose contents can be erased by a mechanism using ultraviolet light and reprogrammed for other purposes.