An EEPROM (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. 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. 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.