EPROM

An erasable programmable ROM (termed as EPROM) is an IC whose memory is of read only type, but which can be reprogrammed by some procedure. It is difficult to rewrite data in an EPROM than in a RAM; the usual process for the erasure involves exposure to ultraviolet. An EPROM IC is recognized by presence of a transparent window with the removable cover, through which ultraviolet is focused to erase the data. The IC should be taken from circuit in which it is used, exposed to the ultraviolet for several minutes, and then is reprogrammed by means of  a special process.

There are EPROMs which can be erased by electrical means. Like IC is called as EEPROM, for electrically erasable programmable read-only memory. These are not required to be removed from circuit for reprogramming.