Why eeprom is better than eprom?
The advantages were "accumulative", so a history of the
development of ROM is best to explain them:
First came ROM - Read-Only Memory. Unlike RAM, ROM could not be
written to but had the advantage that it was non-volatile which
means its contents are permanently there, they do not disappear
when power is removed. But the contents were put there in the
factory, you could not "program" the contents yourself.
Then came PROM - Programmable ROM. With PROM you could, if you
owned a programming machine or "programmer", set the contents of
the PROM yourself, one time, before your put it in the electronic
circuit board.
Next came EPROM - Eraseable PROM - with EPROM if you needed too
you could take the EPROM out of the circuit board, put it in an
EPROM eraser to reset the contents, and then program it again in
the programmer. The EPROM eraser was a small box that the EPROM was
placed inside. When the box was turned on ultra-violet light shined
into the EPROM thorough a small "window" on the top of each EPROM,
erasing the contents.
Finally came EEPROM or E2PROM - Electronically Erasable PROM.
With EEPROM you didn't need the eraser or the programmer! The
EEPROM can be programmed, again and again while it is on the
circuit board, by sending a sequence of signals to certain pins on
the device.