eeprom has the same limitation that flash does: ones made in the 20th century could only survive about 100,000 write cycles, later increased to about a million. it is more expensive than flash, so it is rarely used for storage greater than 128kb. the main difference between eeprom and flash memory is that most eeprom devices can erase any byte of memory at any time. flash memory can only erase an entire chunk, or "sector", of memory at a time. both eeprom and flash are subject to the limitation that only bytes in an 'erased' state can be written, which means that if the user wants to change only one byte of flash, the entire sector must be erased and re-written. this means that flash memory can wear out faster than eeprom. some flash memory can store hundreds of gigabytes, or even terabytes. many are in the form of a pen drive.