If it is set for hibernation mode the contents of memory are written to a disk file.
Description and modification of the different hibernate modes
When the computer goes into sleeping mode, its behavior depends on a power management variable called hibernatemode. The hibernate mode can be set to different values:
- 0 - Default sleep behavior on most Apple computers. RAM is still powered on while sleeping. Wake up is fast. Safe sleep is disabled.
- 1 - Hibernation behavior. System is totally shut down while sleeping. RAM contents are dumped to disk. Wake up is slow.
- 3 - Default behavior on Powerbook HD computers. RAM is still powered on while sleeping. Wake up is fast. Safe sleep is enabled, so RAM contents are also dumped to disk before going to sleep.
Only a single mode can be activated at a time. In order to check what hibernate mode is currently active, the following command can be used in the Terminal application:
pmset -g | grep hibernatemode
In addition, users with administrator privileges can choose the hibernate mode. In order to do so, the following command can be used:
sudo pmset -a hibernatemode X
Replace X with the value of the hibernate mode to set. Enter your admin password when prompted. It will not be echoed.
Also see Energy Saver- About sleep and idle modes in Mac OS X.
