Well, that information is available in the Platform SDK (Windows API).
You can do a search on MSDN.
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The SetSuspendState function suspends the system by shutting power down.
Depending on the Hibernate parameter,
the system either enters a suspend (sleep) state or hibernation (S4).
BOOLEAN SetSuspendState( BOOLEAN Hibernate,
Also, See: Power Management Functions
The SetSystemPowerState function suspends the system by shutting power down.
Depending on the ForceFlag parameter,
the function either suspends operation immediately
or requests permission from all applications and device drivers before doing so.
BOOL SetSystemPowerState( BOOL fSuspend,
There may even be other API functions as well, I haven't looked.