CertiGuide to A+ (Core Hardware)  9  Chapter 0011:  System Memory       9  II  Memory Types

Programmable Read Only Memory (PROM) 1 Electronically Erasable Programmable Read Only Memory (EEPROM)

The EPROM was a significant improvement in ROM technology in that it allowed manufacturers to reprogram their ROM chips with new programs many times. The actual chip has a small window on top through which you can see the actual circuit that contains the program. By exposing this window to ultraviolet light of a specific frequency for a specific amount of time, the program stored in the EPROM would be erased and could then be reprogrammed.

To prevent accidental erasing of the EPROM, this window is typically covered with a small sticker or decal. If you remove this decal from the EPROM, you run the risk of partially or entirely erasing the program on the chip. Reprogramming the EPROM after it has been erased requires special equipment that most PC users do not have access to. Therefore, the industry created a new technology that would allow PC users to erase and reprogram their system ROM without the need of special equipment. This new technology is known as Electronically Erasable Programmable Read Only Memory, or EEPROM.

Programmable Read Only Memory (PROM) 1 Electronically Erasable Programmable Read Only Memory (EEPROM)