On a KNX device, the configuration parametrised by ETS is stored in non-volatile memory (EEPROM or Flash), whereas the runtime states (current values of the Group Objects) live in volatile RAM.

Typical memory layout of a KNX device: Flash/ROM holds the firmware (manufacturer's application program); EEPROM holds the ETS configuration (individual address, parameters, Group Address to Group Object bindings) and persists across mains failure; RAM holds the current Group Object values, runtime state and timers, and is lost on power-down (unless the device's re-initialisation logic explicitly re-reads from EEPROM). That is why, on power-up, a KNX device's outputs may take either a 'default' state (parametrised in ETS) or a 'last known' state depending on the application's configuration.

Always check the 'behaviour after bus voltage recovery' parameter on every actuator during commissioning — it is the single setting that determines whether the building wakes up bright, dark or in chaos after an outage.