Information Technology Reference
In-Depth Information
Tip 121
Put Notebooks in Deep Sleep
Mac notebooks use magnetic case closing mechanisms to keep the lid shut,
rather than physical clasps. This makes opening them much more convenient,
but it also means they can open themselves sometimes, while in a travel bag,
for example. Once open, they can switch themselves on and thus waste battery
life. They might even create a hazard during a flight if the wireless hardware
activates.
If this is a problem for you, you can set your MacBook to hibernate to disk
when the lid is closed, rather than simply go into sleep mode. This turns the
computer off completely, rather than keeping the memory alive with a trickle
of battery power.
Note that this is arguably not a good choice for Macs with a solid-state hard
disk (SSD), such as MacBook Air computers. It will mean that every time the
computer powers down, a multigigabyte hibernation file is saved to the hard
disk, usually slightly larger than the size of your computer's RAM (that is,
4GB or 8GB). In theory, this can wear out SSD more quickly.
Setting Up
This tip changes a firmware setting for the entire computer, so it will affect
all users.
Open a Terminal window, and type the following:
SUDO PMSET -A HIBERNATEMODE 25
You'll need to enter your login password when prompted. The changes should
take effect right away.
Putting to Sleep and Waking
Give your changes a try by closing the lid and waiting a minute or two for it
to hibernate. Then wake your computer (remember, you'll now need to press
the power button each time). Waking a hibernated computer takes a few
seconds longer as the RAM contents are read in from disk, but it's still fast
enough for everyday use.
