EEPROM is a type of non volatile memory used in many modern electronic devices that wish to store memory for a specific amount of time, and also want it to be erased at given times. EEPROM or E2PROM is an acronym for Electrically Erasable Programmable Read Only Memory. Earlier Erasable Programmable Read Only Memory (EPROM) chips contained {or did not, if the manufacturer wished to make One Time Programmable (OTP) chips} a tiny quartz window that allowed Ultraviolet (UV) light to enter the chip and erase the non volatile memory stored in it. EEPROM data can be erased electrically (as the name itself suggests) by the phenomenon of field electron emission. This technique allows the ROM to retain its data consistently, and also be ready for a re-programming when needed, or an erasure if necessary.
EEPROM’s were first designed by George Perlegos at Intel. In 1983 he designed an EPROM chip that had thin gate oxide layer atop the semiconductor layer so that it could erase its own data when a high voltage is passed through it, without the need of a UV source, i.e. without a quartz window specifically designed to erase the data. Though rudimentary, this design was exploited by him when he left to form his own Seeq Technology and developed the first on device charge pumps used for data erasure and re-programming that also developed a very high voltage from a low input voltage – the exact kind of device that would power and pre process an EEPROM’s functions.
EEPROM’s are of both serial bus and parallel bus types and have typical instructions coded into them. Though they can be erased and programmed, the number of times this can be done is limited as the oxide re-writing layer can be easily destroyed by frequent erasure and re-programming. This is why EEPROM’s are used in cell phone ROM’s and BIOS coding chips which are not frequently formatted, and thus are safe from frequent reprogramming and the corresponding oxide layer destruction.
EEPROM’s also form the basis of Flash drives which are written and rewritten many times to be classified generally as EEPROM’s. These drives function differently to allow for a safe way of storing and restoring data without harming the internal mechanisms and the semiconductors. Flash drives are optimised for a large number of cycles of storage and retrieval and most have a read-write cycle of a million times; enough for a lifetime of storage and retrieval.
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