S.M.A.R.T. в Linux

Power-On Hours Count
The raw value reports two values: the first
4 bytes report the cumulative number of
power-on hours over the life of the device,
the remaining bytes report the number of
milliseconds since the last hour increment.
The On/Off status of the Device Initiated
 Power Management (DIPM) feature will
 affect the number of hours reported. 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.