Apple supports three main types of sleep modes for desktops and portables. The three modes are Sleep, Hibernation, and Safe Sleep, and they each work slightly differently.
The Mac’s RAM is left powered on while it’s sleeping. This allows the Mac to wake up very quickly, because there’s no need to load anything from the hard drive. This is the default sleep mode for desktop Macs.
In this mode, the contents of RAM are copied to your drive before the Mac enters sleep.
Once the Mac is sleeping, power is removed from the RAM. When you wake the Mac up, the startup drive must first write the data back to the RAM, so wake time is a bit slower. This is the default sleep mode for portables released before 2005.
The RAM contents are copied to the startup drive before the Mac enters sleep, but the RAM remains powered while the Mac is sleeping. Wake time is very fast because the RAM still contains the necessary info. Writing the RAM’s contents to the startup drive is a safeguard. Should something happen, such as a battery failure, you can still recover your data.
Since 2005, the default sleep mode for portables has been Safe Sleep, but not all Apple portables are capable of supporting this mode. Apple says that models from 2005 and later directly support Safe Sleep mode; some earlier portables also support Safe Sleep mode.
Find Out Which Sleep Mode Your Mac is Using
You can find out which sleep mode your Mac is using by opening the Terminal application, located at /Applications/Utilities/.
When the Terminal window opens, enter the following at the prompt (you can triple click the line below to select it, then copy/paste the text into Terminal):
pmset -g | grep hibernatemode
You should see one of the following responses:
- hibernatemode 0
- hibernatemode 1
- hibernatemode 3
- hibernatemode 25
Zero means normal sleep and is the default for desktops; 1 means hibernate mode and is the default for older portables (pre 2005); 3 means safe sleep and is the default for portables made after 2005; 25 is the same as hibernate mode, but is the setting used for newer (post 2005) Mac portables.
A few notes about hibernatemode 25: This mode has the potential to maximize battery runtime, but it does so by taking longer to enter hibernation mode, and longer to wake up from hibernation. It also forces paging of inactive memory to disk before hibernation occurs, in order to create a smaller memory footprint. When your Mac wakes from sleep, the inactive memory that was paged to disk isn’t restored to memory right away; instead; the inactive memory is restored when needed. This can lead to apps taking longer to load, and drive paging to occur well after your Mac has wakened from sleep.
However, if you really must squeeze out every joule of energy from your Mac’s batteries, this hibernation mode may be helpful.
Besides sleep, your Mac can enter a standby mode to conserve the battery’s charge. A Mac portable can remain in standby for up to thirty days under ideal conditions. Most users with batteries in reasonable shape and fully charged could see 15 to 20 days of standby power.
Mac computers from 2013 and later support standby operations. Standby is entered automatically if your Mac has been asleep for three hours, and your Mac portable has no external connections, such as USB, Thunderbolt, or SD cards.
You can exit standby by opening the lid on your Mac portable, or tapping any key, plugging in the power adapter, clicking the mouse or trackpad, or plugging in a display.
If you keep your Mac in standby mode for too long a period, the battery can be completely discharged, requiring you to attach the power adapter and restart the Mac by pressing the power button.
Changing Your Mac’s Sleep Mode
You can change the sleep mode your Mac is using, but I don’t advise it for older (pre-2005) Mac portables. If you try to force an unsupported sleep mode, it may cause the portable to lose data when sleeping.
Even worse, you may end up with a portable that will not wake up, in which case, you’ll have to remove the battery, then reinstall the battery and operating system. If my portable didn’t support Safe Sleep, I’d prefer the reassurance of hibernating over a quicker wakeup from standard sleep mode.
If your Mac isn’t a pre-2005 portable, or you want to make the change anyway, the command is:
sudo pmset -a hibernatemode X
Replace X with the number 0, 1, 3, or 25, depending on which sleep mode you wish to use. You will need your administrator password to complete the change.