Lenovo ThinkPad R51e Series Hardware Maintenance Manual page 43

Also, the computer goes into hibernation mode
automatically in either of the following conditions:
v If a "hibernation time" has been set on the timer, and if
the user does not do any operation with the keyboard,
the TrackPoint, the hard disk drive, the parallel
connector, or the diskette drive within that time.
v If the timer conditions are satisfied in suspend mode.
When the power is turned on, the computer returns from
hibernation mode and resumes operation. The hibernation
file in the boot record on the hard disk drive is read, and
system status is restored from the hard disk drive.
In R51e, you can also use the ThinkVantage Productivity
Center to put the computer in hibernation mode.
Related service information
General descriptions
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