Flash memory

Flash memory is a form of EEPROM that allows multiple memory locations to be erased or written in one programming operation. Normal EEPROM only allows one location at a time to be erased or written. All types of flash memory and EEPROM wear out after a certain number of erase operations.

Flash memory is made in two forms: NOR flash and NAND flash. The names refer to the type of logic gate used in each storage cell. NOR flash was the first type to be developed, and was invented by Intel in 1988. It has long erase and write times, but has a full address/data (memory) interface that allows random access to any location. This makes it suitable for storage of program code that needs to be infrequently updated, as in digital cameras and PDAss. Its endurance is 10,000 to 100,000 erase cycles. NAND flash from Toshiba followed in 1989. It has shorter erase and write times, higher density and lower cost per bit than NOR flash, and ten times the endurance, but its I/O interface allows only sequential access to data. This makes it suitable for mass-storage devices such as PC cardss and various memory cards like Compact Flash and Secure Digital media.