Compaq Armada 7400 Reference Manual page 60

Hibernation is a safeguard condition in which all information in
system memory is saved to the hard drive and power to the
computer is turned off. When you resume your work, your
information is returned to the screen exactly where you left off.
When Hibernation is initiated, no information is lost. There is
no limit to the amount of time the computer can remain in
Hibernation, since the computer is turned off and there is no
drain on the battery pack.
Hibernation can be used as a placemarker. For example, it is
useful when you're making a presentation away from the
office. You can do all the preparation in advance, mark your
place by initiating Hibernation, and be ready to make your
presentation as soon as you arrive.
Hibernation is a safeguard feature that saves information
should the computer reach a critical low battery condition
while it is left unattended.