Problem
- users can't/shouldn't distinguish sleep and hibernation
- suspend to RAM (S3) is not robust against power loss
- we don't have anything that can reliably replace a full power off
Relevant Art
Windows Vista does not use a hybrid suspend. It seems to wake from S3 and enter S4 as necessary.
http://www.microsoft.com/windows/windows-vista/features/fast-sleep-and-resume.aspx
Apple Mac OS X seems to perform a true "hybrid suspend". In that it means suspends state to disk before it suspends to ram.
Discussion
According to Matthew Garrett (Oct 2008): "So what we have *now* is all the technology to do S3, resume at some later point and then either return to S3 or if power is low, change to S4. Why we *can't* do that under any circumstances by default is that on at least 20% of systems, resume will fail for one bullshit reason or another. We understand all those reasons, but it's going to be at least a year until they're fixed."
Can we wake from S3 on a low battery condition or only after an amount of time? Matthew says that we can "make a handwavy and conservative guess at the rate of power drain, set the alarm to wake us before 0 [power]. When we wake, recalibrate that guess and either go back to S3 or enter S4."
We would need to do more work to make Hibernate/S4 faster and more reliable.
Matthew will hopefully write up some more information about this in his blog.