A couple weeks ago, Matt wrote a great Tech Tail regarding Safe Sleep. I wanted to touch on this topic again, because there is a choice for the MacBook owners out there as to how they want their machine to behave when the lid is closed.

The basic function of Safe Sleep is to dump the contents of memory (RAM) to the hard disk when you put your computer to sleep. This also allows the computer to even have it’s power removed entirely for a short time, and when plugged into power, the contents of memory are restored from the hard disk back to the RAM. Similar to ‘hibernate’ mode in Windows. This doesn’t mean it’s not using any power. However, it’s using a negligible amount.

As a portable user who moves your machine around a lot, but never lets the battery go completely dead, you may not desire Safe Sleep. It can lead to premature failure of your hard disk if you move the machine before it’s fully asleep because it can take up to a minute for your system to write 4GB of memory to the hard drive (and some new machines have an 8GB maximum of system memory).

When I close my laptop, it’s because I’m ready to leave. I often don’t want to wait a minute before moving the machine. If I do have to move it in a hurry, I also don’t want to risk damaging the hard drive by swinging the laptop around while it’s writing 4GB to the hard disk.

Pros to Safe Sleep:

  • Reduced power consumption while sleeping
  • Data in RAM is safe if battery dies

Cons to Safe Sleep:

  • Increased power usage while writing your RAM onto the hard drive
  • Wait time after closing the lid, but before moving the machine (sometimes up to one minute or longer)

How do I shut it off?

IMPORTANT: The commands for Leopard and Tiger are different. Please make sure you are running the correct OS before running these commands by going to the Apple Menu and selecting About This Mac. Also, your mileage may vary and we beg you to have a current backup of your system before trying this out.

Open Terminal, which is under Macintosh HD/Applications/Utilities (don’t worry, this isn’t complicated)

For Leopard (10.5): Copy and paste, then press return: sudo pmset -a hibernatemode 0

For Tiger (10.4): Copy and paste, then press return: sudo pmset -a hibernatemode 0 followed by sudo nvram “use-nvramrc?”=false


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