EEPROM stands for Electrically Erasable Programmable Read-Only Memory. EEPROM is a type of non volatile memory which is used in computers or electronic devices to maintain the data when power is turned off but in case SRAM or DRAM information may be lost when power is switched off. To store the larger amount of data, a special type of EEPROM is used known as flash memory which is more economical in comparison to EEPROM devices.
History :-
In1983, George Perlegos developed the Intel 2816 at Intel, which was based on earlier technology EEPROM, but now we are using a thin gate oxide layer because the chip could erase its own bits without an ultra violet source. George Perlegos and others left to form Seeq Technology, which used on charge pumps devices to supply the high voltages which is necessary for EEPROMs.
Types of EEPROM :-
There are two types of EEPROM
1. Parallel Bus 2. Serial Bus
Parallel Bus :-
Parallel EEPROM devices typically have an address bus wide enough to cover the complete memory and 8-bit data bus. Most devices have chip select (CS) and write protect pins (WR). Some Microcontroller have integrated parallel EEPROM.
Operation of a parallel EEPROM is simple and fast in comparison to serial EEPROM, but these devices are larger due to the higher number of pins (28 pins or more) and have been decreasing in popularity in favor of serial EEPROM or Flash.
Parallel EEPROMs are used in applications such as POS terminals, industrial controllers, LAN adapters, telecommunication switches, cellular phones and modems.

Serial Bus :-

Serial EEPROM works in three modes : OP-Code Phase, Data bus and Address Phase.The OP-Code is usually the first 8-bits input to the serial input pin of the EEPROM device followed by 8 to 24 bits of addressing depending on the depth of the device, then data to be read or written.
Serial EEPROM products are used in many applications to store user reconfigurable data. Common applications are disk drives, modems, cellular phones, VCRs, CD players, hearing aids, PCMCIA cards, cordless phones, laser printers, computers and pagers.
Comparison with EPROM and EEPROM/Flash :-

EPROMs can not be erased electrically, and are programmed through hot carrier injection onto the floating gate. Erase is possible with the help of an Ultra Violet light source, although in practice many EPROMs are encapsulated in plastic that is opaque to Ultra Violet light, and are "one-time programmable".

EEPROM can be programmed and erased electrically using field emission generally known in the industry as "Fowler-Nordheim tunneling".
Mostly NOR Flash memory is a hybrid style-programming is through hot carrier injection and erase with the help of Fowler-Nordheim tunneling.

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