Sleep and Hibernation Modes – What’s the Difference?

Over the years the humble shut down menu in Windows has been home to a number of options since it appeared back in Windows 95. If you can cast your mind back fifteen years, the usual suspects in the menu were:

• Shut down the computer
• Restart the computer
• Restart the computer in MS-DOS mode
• Close all programs and log on as a different user

The menu soon evolved to include other options including:

• Lock
• Switch User
• Stand by (or Sleep in more recent versions of Windows)
• Hibernate

Whilst the original four options plus the top two from the second group may have been fairly obvious to many people the distinction or meaning of the last two options (sleep and hibernate) are often unknown. As such, I thought I would point out the high level differences between to two.

Sleep mode essentially puts your computer into a low power state without switching completely it off. On laptops, sleep mode can be triggered by closing the lid and, on some models, exited by reopening the lid. Otherwise, pressing the power button will wake it up again. Computers may also have power profiles that will put a computer to sleep if it has not been used for a given length of time to reduce power consumption and battery life. The main risk with sleep mode is if the computer completely loses power then the state of the current session held in RAM is lost (so if you have valuable documents open you should save them and save often). Thankfully, recent versions of Windows will force a computer into a hibernation mode to help prevent that from happening.

This leads us to hibernation mode. In the traditional sense, hibernation mode involves writing the contents of RAM to disk and then shutting down the computer. In this mode the computer will use no power and, upon turning the computer back on, resume from the point of hibernation after reading the former contents of RAM back into memory from disk. I find this particularly good for my work laptop as it takes up to five minutes for all of the security policies to be downloaded and enforced before I can login and wait for it to stop grinding coffee for me to actually use it. I’d estimate it saves me between twenty to forty minutes of time a week sitting around waiting for my computer to be in a usable state.

In Windows Vista and 7 a new mode called “hybrid sleep” was introduced which, as the name suggests, is a hybrid concept of sleep and hibernation modes. When engaged, the contents of RAM are maintained in RAM but also copied to disk to mitigate against data loss due to a loss of power. If power is lost, turning the computer back on will see it resume from the point of hybrid sleep.

One thing to bear in mind with hibernation and hybrid sleep modes is that they can be slow to engage as it must write from RAM to disk which itself is slow. Also, the more RAM you have in your computer the more data you will be writing to disk (which is a bit of a bother in my system as it has 12GB). This also means that you will have that same amount of space reserved on your system drive which cannot be used for anything else. If space is at a premium (particularly if you have a small SSD as your system drive) then you will need to work out what is more important, space or hibernation/hybrid sleep modes.

Hopefully, now you know the difference between all of these low power modes!