Vista Notes, Episode #2: Sleep vs. Hybrid Sleep

In this second episode of my ongoing series entitled "Vista Notes" (wherein I expound on an interesting feature I've found in my daily use of Windows Vista), I wanted to discuss the new "Sleep" and "Hybrid Sleep" features.

To discuss these modes, we first need to define two other terms:


Standby is Windows' name for ACPI mode S3. In this mode the PC shuts down most components, but leaves enough power going to keep the main memory powered. 
Pros: Goes into standby fast. Comes out fast
Cons: Uses up a small amount of power. If the battery dies (or is removed), all data in memory will be lost.


Hibernate is Windows' name for ACPI mode S4. In this mode, the PC saves the contents of RAM to disk (in a file called hiberfil.sys), and then turns itself off completely.
Pros: Slow to go into Hibernate. Slow to come out.
Cons: Uses up no power. Computer can lose all power and still recover.


As many people know (in particular, thanks to a recent article by Joel Spolsky), Windows Vista promotes a feature called "Sleep".

Here’s what happens with normal Sleep on Vista.

  • First the laptop goes into Standby.
  • Then, if the battery gets into a critical state, or a certain time passes (configurable in the Power Options CPL), the laptop will wake briefly from Standby and go into Hibernate (which doesn’t use battery life).

This is the default behavior on a laptop. The idea is that under most circumstances, your laptop will go into power-saving mode fast, and come back out fast (you can be back to your desktop in 2 seconds or less -- about as long as it takes to open the lid of the laptop). 

It's also safe, because it'll save your data if the battery goes critical.

Hybrid Sleep

Hybrid Sleep is designed for desktops, not laptops. In Hybrid Sleep mode, when you click Sleep, the computer does two things:

  • Saves all of your data to disk as if it was going into Hibernation
  • Goes into standby. It stays in standby permanently (unless you change the setting in the Power Options CPL to make it Hibernate fully at some point).

The idea is that this is better than normal sleep because if the desktop loses power while in sleep mode ("cat chews through the power cable" scenario), it will still be able to recover because all of the data was saved (this confused me at first until I remembered that desktops don’t have batteries, so there is no way for them to “wake up from standby and go into hibernate mode” if power is lost).

It’s also better than using Hibernate on the desktop because, unless you lost power in the interim, you’ll get the fastest-time-to-desktop behavior of standby.

On the downside, going into Hybrid Sleep mode is slower than normal Sleep mode (because it as to do all of the saving-to-disk as if it was going into Hibernate), which is why it is off-by-default on laptops. It’s also not useful on a laptop unless you’re in the habit of yanking out the battery from the laptop completely while it’s in sleep-mode.


Fun stuff.

- Sean

 Update: Wierd. Jim wrote a post on Vista power saving for the Vista Team blog, which covers these two features (and others) in detail. He scooped me.