ROM (Read Only Memory) is nonvolatile (retains memory after power loss); most common use is the
BIOS. PROM (Programmable Read Only Memory) – Can only be written once, normally at the factory.
EPROM (Erasable Programmable Read Only Memory) – Can be erased (flashed) and written many times, by
shining an ultraviolet light (flash) on a small window on the chip (normally covered by foil).
EEPROM (Electrically Erasable Programmable Read Only Memory) – These are Electrically Erasable, you
can use a flashing program. This is still called Read Only. The ability to write to the BIOS makes
it vulnerable to attackers.