EPROM is a special type of memory that retains its contents untill it is exposed to ultraviolet light. The ultraviolet light clears its contents, making it possible to reprogram the memory.
An EPROM differs from a PROM in that a PROM can be written to only once and cannot be erased. EPROM s are used widely in personal computers because they enable the manufacturer to change the contents of the PROM before the computer is actually shipped. This means that bugs can be removed and new versions installed shortly before delivery.