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I am quite used to the fact, that MacOS X does a lot abracadabra internally to provide the best user experience ever, but I also used to understand all that happens. With my pristine MBPr (3 battery loadcycles) I got lost. There are at least two things that I do not understand.

First of all my pmset -g configuration is as follows (note hibernatemode is off):

Currently in use:
 standbydelay         4200
 standby              1
 womp                 1
 halfdim              1
 hibernatefile        /var/vm/sleepimage
 gpuswitch            2
 darkwakes            1
 networkoversleep     0
 disksleep            10
 sleep                10
 hibernatemode        0
 ttyskeepawake        1
 displaysleep         10
 acwake               0
 lidwake              1
  1. When I was using my notebook at the very beginning it was running on batteries until almost drained. At about 1% I rebooted it, but instead of rebooting it presented me a nice empty battery pictogram (just one you may know from iOS devices). I pushed power-on button several times just to see the very nice pictogram again. I left the notebook then and started looking for a charger. Accidentaly after a few seconds MBPr powered itself (!) on. Still on battery! I pressed Option and waited on boot screen until it turned off again - but this lasted for long minutes.

  2. Having it recharged to 100% I used it on battery again. This time I didn't notice that it went down to 0% while I stil had my system booted and many applications open. I glanced a "running on reserve battery power" warning and screen went blank. Pushing power-on button - no action. I simply put a charger in and went to sleep. In the morning another suprise: I open the lid and see that the system didn't actually shut off. It is up and all my applications are still running. So at 0% battery it simply went to some "sleep" mode.

My guessing is that either battery is somehow uncalibrated and provides more power than the system expects from it, or MBPr with ML is keeping some additional non-reported reserve of power below displayed 0%. Or am I wrong? It's a pity that the nice sleep indicator was removed from the chasis - without you never actually know what your system is doing right now.

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The best part is that OS X kind of dump your current system to the disk so it can come back right to where it went out of power. Kind of how most iOS apps works when put to background. Another interesting thing is that I experienced "shutdown" by lack of power but the Mac doesn't shut down totally. The sleep light was still pulsing and such. –  Hoshts Aug 16 '12 at 9:19
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From what I know - disabling hibernatemode causes OS X not to dump memory to disk. –  Kuba Wyrostek Aug 16 '12 at 9:26
    
I just read about how hibernate to be unnecessary as the HFS+ keeps track of changes and updates to the drive. –  Hoshts Aug 16 '12 at 9:33
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1 Answer 1

macbooks generally hibernate (save your ram's state to your hdd) when the battery is too low.
to do that efficiently (without losing data) there's an internal threshold that keeps some energy for the system to save state.

in general, you don't shut down (as in "windows is shutting down") your mac. you either let it go to sleep after some time or just close the lid (and trigger hibernation). you can even trigger hibernation from the apple menu.

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Sorry but this is not true here. I made a statement on hibermantemode on purpose. I even do not have hibernation data file on my drive (/var/rm/sleepimage). –  Kuba Wyrostek Aug 16 '12 at 11:02
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