EPROMs

EPROM (Erasable Programmable Read-Only Memory) is a type of non-volatile memory (meaning that its data is retained even after power is turned off) which can be erased by exposing to a strong ultraviolet light source (about 20 minutes) and re-programmed electrically. EPROMs will have a transparent fused quartz window on the top of the IC through which the UV light can be applied for erasing the chip. Since the whole chip is exposed to UV light during erasing, the whole memory is erased same time.