Definition: EEPROM (pronounce as "E-E-PROM") stands for Electrically Erasable Programmable Read-Only Memory. It is a non-volatile ROM chip which used for storing a small amount of data in computers or some other electronic devices. Through EEPROM, an individual byte of data can erase and reprogrammed entirety, not selectively by the electrical voltage.
EEPROM was developed by George Perlegos in 1978 at Intel. However, for the first time, it was developed by Eli Harari in 1977 at Hughes Aircraft. EEPROM used as a replacement for PROM (Programmable Read-Only Memory) and EPROM (Erasable Programmable Read-Only Memory).
For modification in the EEPROM chip, there is no need of removing the chip from the computer. EEPROM perform read and write cycle very slowly as compared to the read and write cycles of RAM. Here, erase and write operations are performed by byte per byte.
EEPROM is a distinct type flash memory that can store large-capacity (static or semi-static) "data" bits or "program" bits than conventional EEPROM devices.
Types of EEPROM Memory
There are two main types of memory are available from the family of EEPROM memory devices.
Serial EEPROM Memory
The operation of serial EEPROM memory is complicated,anddata transferred serially. So, this makes them slow as compared to the parallel EEPROM. Also, serial EEPROMs are less dense and are much cheaper.
A serial EEPROM protocol is made up of three phases:
• OP-Code phase
• Address Phase
• Data Phase
Parallel EEPROM memory
The operation performed by parallel EEPROM memory is much faster as compared to the serial EEPROM memory. Parallel EEPROM memory is much denser and reliable than the serial EEPROM memory. Also, parallel EEPROM memory is compatible with the EPROM and flash memory devices. Parallel EEPROMs are more substantial, and due to its cost, there is the very low popularity of parallel EEPROMs.
EEPROM memory failure modes
There are two failure modes due to which memory devices can fail, which explained below:
• Data retention time
As we know that data retention time is of much importance and it is insufficient in case of EEPROM, because the electrons which injected into the floating gate may sometime drift through the insulator. The reason behind the drifting is that the insulator is not a perfect insulator. Due to which the charge gets lost, and the data get erased. So this is the reason that the manufacturers guarantee the data retention of 10 years.
• Data endurance
During the rewrite operations of the EEPROM memory, the cell got stuck into the programmed state. So for this, the manufacturer has to specify the minimum number of rewrite cycles and the rewrite cycles can be maximum 1 million.
Advantages of EEPROM Memory
• We can reprogram EEPROM infinite number of times.
• The method of erasing the data is immediate and is electrical.
• We can program and erase the contents of EEPROM without removing the chip from the computer.
• There is no requirement of additional equipment for changing the contents.
• We can erase the data on EEPROM byte bybyte basis.
Disadvantages of EEPROM Memory
• There is a requirement of different-2 voltages for erasing, reading and writing the data onto the EEPROM memory.
• EEPROM has limited retention time.
• It is expensive as compared to the PROM and EPROM.
• The serial EEPROM memory requires more time for execution.