Having problems waking up your European iMac from sleep? Chanses are your computer switched from sleep to hibernation mode without you knowing because of a European Union energy savings regulation, specificly the Lot 6 of the Energy-related Products Directive.
Some years ago there was widespread concern that hundreds of millions of electrical devices are no longer switched of completelly but instead put in stand-by mode where they still consume electricity around the clock. This was especially a consern regarding televisions and computers. As a result, the European Union introduced several regulations on the subject. One, known as "Lot 6" refers to stand-by modes in home appliances:
"The objective of the eco-design requirements for standby and off-mode is to ensure lowest possible energy use for small and large household appliances and electronic products in passive standby and off modes."
The main requirements are:
- Max 1 W power for passive standby and off-mode starting in 2010
- Max 0.5 W starting from 2013
In order to complie with this regulation, Apple has introduced a power management feature called "auto power off" in European sold iMacs and possible other Macs aswell such as the Mac Mini and Mac Pro. Although not visible in the OSX Power panel in Settings, you can check for it using the "pmset" command line application. Using "pmset -g" will show you the current settings. If "autopoweroff" is set to 1, that means your computer is configured to automatically go from sleep mode to hibernate after a predefine time. The default time is 4 hours (14400 seconds). The time is defined by the "autopoweroffdelay" setting - acording to Apple's documentation the number is minutes but it probably is seconds.
In theory this is a reasonable feature. Normal stand-by, also known as "suspend to RAM" or "sleep state S3" means that the screen, disk and CPU are shut down and minimum power is supplied only to RAM to keep everyting as it was prior to sleep, that way, when you wake up the computer you can immediately continue where you left of. But this mode means the computer continues to draw power.
Hibernation, also known as "suspend to disk" or "sleep state S4" writes the content of the computer's RAM memory to a file on the hard drive and then shuts down the computer entirely. The computer then has to be woken up using the power button and the hibernation data read from the file on the hard drive into memory and then you can continue where you left of.
So what is wrong with letting your Mac power down completely if you haven't used it in four hours - starting it up will only take a few more seconds and you will not loose anything? The problem is that this does not always work as it should and many Mac users find that waking up the computer is difficult and surprisingly slow. Some times you have to press the power button 10 seconds for the Mac to react at all. Some times you have to unplug the computer and plug it in again before it will start.
You can recognize that your Mac is waking up from hibernation if you see a grey screen with only a progress bar when the computer wakes up and it takes several seconds. Waking up from normal sleep mode should take no more than one second.
If your Mac has problems getting out of sleep mode and pmset shows that you have autopoweroff enabled you can disable it yourself and see if that helps. You do this by running the command:
"sudo pmset -a -autopoweroff 0"
Sudo gives you "super user" rights which is needed for this operation, -a means it refers to all power stats (on ac power and on battery power).
Further information about the pmset command can be found att Apples developer site:
Although there is a similar initiative in the US called the One Watt Initiative, this "feature" seems to be active only in European sold Apple computers.
I am not aware of how PC manufacturers have handled this but there it is more of a hardware problem handled by the ACPI implementation on the main board and not by the operating system although there are power settings in Windows as well.