According to the pmset man page,
hibernatemode = 3 (binary 0011) by default on supported portables. The
system will store a copy of memory to persistent storage (the disk), and
will power memory during sleep. The system will wake from memory, unless
a power loss forces it to restore from disk image.
But then also
standby causes kernel power management to automatically hibernate a
machine after it has slept for a specified time period. This saves power
while asleep. This setting defaults to ON for supported hardware. The
setting standby will be visible in pmset -g if the feature is supported
on this machine.
standby only works if hibernation is turned on to hibernatemode 3 or 25.
(which it is by default on supported portables)
standbydelay specifies the delay, in seconds, before writing the hibernation image to disk and powering off memory for Standby.
On my machine, with settings that I believe are default, when I type pmset -g |grep standbydelay I get the result of 4200, meaning that after 70 minutes of sleep, the machine cuts power to the memory and restores from the memory image saved to the hard drive.
If your settings do not look like this, the pmset command just might be your new friend.
