What is the X in X-mas?
(FEPROM, "flash memory") A kind of non-volatile storage device similar to EEPROM, but where erasing can only be done in blocks or the entire chip.
In 1995 this relatively new technology started to replace EPROMs because reprogramming could be done with the chip installed. At that time FEPROMs could be rewritten about 1000 times.
Like EAPROM and ferro-magnetic material, FEPROMs rely on FN tunnelling. Some flash memory supports block erase.