The status of Device Initiated Power Management (DIPM) feature will affect the number of hours reported by the Power-On Hours Count attribute:
- If DIPM is turned on, the recorded value for power-on hours does not include the time that the device is in a "slumber" state.
- If DIPM is turned off, the recorded value for power-on hours should match the clock time, as all three device states are counted: active, idle and slumber.”
DIPM is part of the AHCI Link Power Management feature, which is usually enabled and hidden from the advanced power plan options in Windows*.