PROM - (programmable read-only memory) is a memory chip on which data can be written only once. Once a program has been written onto a PROM, it remains there forever. Unlike main memory, PROMs retain their contents when the computer is turned off.
The difference between a PROM and a ROM (read-only memory) is that a PROM is manufactured as blank memory, whereas a ROM is programmed during the manufacturing process. To write data onto a PROM chip, you need a special device called a PROM programmer or PROM burner. The process of programming a PROM is sometimes called burning the PROM.
EPROM - (erasable programmable read-only memory) is a special type of PROM that can be erased by exposing it to ultraviolet light. Once it is erased, it can be reprogrammed. An EEPROM is similar to a PROM, but requires only electricity to be erased.
EEPROM - (electrically erasable programmable read-only memory). Pronounced e-e-prom, an EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge. Like other types of PROM, EEPROM retains its contents even when the power is turned off. Also like other types of ROM, EEPROM is not as fast as RAM.
A special type of EEPROM, referred to as flash memory or flash EEPROM, can be rewritten while it is in the computer rather than requiring a special device called a PROM reader. This is what most of you will have.
This information comes from PCWebopedia.
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