EEPROM
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An EEPROM (E²PROM, E2PROM), or Electrically-Erasable Programmable Read-Only Memory, is a non-volatile storage chip used in computers and other devices. Unlike an EPROM, an EEPROM can be programmed and erased multiple times electrically. Each bit is set by quantum tunneling electrons across a thin dielectric barrier. The electron flow through the barrier causes defects to build up in the thin layer of silicon dioxide, leading to its wear known as tunnel oxide degradation. Because of this, it may be erased and reprogrammed only a certain number of times. Write/erase cycle lifetimes range from 100,000 to 10,000,000, but an EEPROM can be read from an unlimited number of times. The write and erase operations require considerably high voltage (12 to 20V), which in low-voltage devices (3.3V, 5V) is created on-chip by a charge pump; the voltage requirements lead to high power consumption during writes, causing a potential vulnerability for differential power analysis when used in smart cards, if countermeasures are not used. EEPROMs typically have relatively slow write times.
Serial EEPROMs acome in a range of capacities from few bytes to over 64 kilobytes. They are typically used to store configuration parameters, and in modern computers they replace the CMOS RAM for BIOS data.
Flash memory is a later form of EEPROM. In the industry, there is a convention to reserve the term EEPROM to byte-wise writable memories compared to block-wise writable flash memories. EEPROM takes more die area than flash memory for the same capacity because each cell usually needs both a read and a write transistor where flash memory needs only one.
Newer technologies are appearing, for example FRAM and MRAM, slowly replacing EEPROMs in some applications.
External links
- Everything a System Engineer Needs to Know About Serial EEPROM Endurance (http://ece-www.colorado.edu/~mcclurel/man537.pdf)da:EEPROM
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