 It is unclear how long flash memory will persist under archival conditions i.e., benign temperature and humidity with infrequent access with or without prophylactic rewrite.Datasheets of Atmel's flash-based "ATmega" microcontrollers typically promise retention times of 20 years at 85 °C (185 °F) and 100 years at 25 °C (77 °F).An article from CMU in 2015 writes that "Today's flash devices, which do not require flash refresh, have a typical retention age of 1 year at room temperature."