Device is on and running. It is receiving full power from the system, and is delivering full functionality to the user. Buses in D1 cannot do anything to the bus which would force devices on that bus to lose context. Attains greater power savings than D1. Device is off and not running.
Device context is lost.
Power may be removed from the device. Any device context lost must be restored by the device driver when returning the device to the D0 state. Recommended latency to return to D0 is less than 5 seconds. For ATA devices, this state is invoked by the Standby Immediate command. This state is not defined for storage devices.