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Fix possible hibernation activation in desktop Macs
Authored by: slswift on Jun 04, '12 08:33:24AM

I just found my Mac mini with 10.7.4 in hibernatemode = 3. Reading the manage on pmset, it says that state will power down the memory, at least in a laptop. Does anyone know if it would power down memory in a desktop machine?

RAM can be a pretty big power drain and heat generator. I might think about leaving my desktop at level 3 if it meant a possibly cooler sleep state.



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Fix possible hibernation activation in desktop Macs
Authored by: arcticmac on Jun 04, '12 08:54:02AM

To quote the manpage (emphasis mine):

     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.

hibernatemode 3 does "powers" not "powers off" the RAM. It simply makes it so that if power is lost while the machine is asleep, that the state can be restored from the sleepimage, which shouldn't be of much concern on a desktop.

If you want to do a real "hibernate" (i.e. power off after sleeping to disk), you want hibernatemode=25 according to the manual. Note that this will make your computer take _much_ longer to wake from sleep. With fast restore in 10.7, you'd probably be better off shutting it down in my experience.



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Fix possible hibernation activation in desktop Macs
Authored by: slswift on Jun 04, '12 08:57:08AM

Not enough coffee this morning.
I completely misread that. Makes more sense. Thanks for clearing that up.



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