EPROMs had to be erased completely before they could be rewritten. Toshiba began marketing flash memory in 1987. They differ at the circuit level depending on whether the state of the bit line or word lines is pulled high or low: in NAND flash, the relationship between the bit line and the word lines resembles a NAND gate in NOR flash, it resembles a NOR gate.įlash memory, a type of floating-gate memory, was invented at Toshiba in 1980 and is based on EEPROM technology.

Both use the same cell design, consisting of floating gate MOSFETs.

The two main types of flash memory, NOR flash and NAND flash, are named for the NOR and NAND logic gates. Flash memory is an electronic non-volatile computer memory storage medium that can be electrically erased and reprogrammed.