Flash memory
Flash memory is non-volatile, retaining its contents even when the power is switched off. It is stored on floating-gate MOSFET memory cells, and can be erased and reprogrammed as required. This makes it useful in PLDs that may be reprogrammed frequently, such as PLDs used in prototypes. Flash memory is a kind of EEPROM that holds information using trapped electric charges similar to EPROM. Consequently, Flash memory can hold information for years, but possibly not as many years as EPROM.