Why does my screen go black when an emergency hibernation is in progress?

Sometime last year a customer wanted to know why the screen goes black when the system automatically hibernates due to critically low battery power. Shouldn't there be some sort of feedback to tell the user, "Hey, like, I'm hibernating, don't worry"?

The power management folks explained that they turn off the screen for a reason: They're trying to save your data while they still can. When the system gets the "Oh no, the battery is about to die!" notification from the hardware, there's no time to lose, and even less power to waste. Keeping the screen lit takes a lot of power, so turning it off might make the difference between a successful hibernation and loss of data.

Mind you, this doesn't all happen without fair warning. Before the battery goes critical, you will get a low battery warning balloon saying "Oh dear, things are getting pretty bad, you really should wrap things up before I'm forced to stop the car!"

It so happens that this particular customer had a system with a buggy BIOS that fails to notify the operating system of changes in power level with sufficient granularity. The power level went from "okay" straight to "critical" with no steps in between. As a result, Windows doesn't find out about the low battery level until it's already at critically low levels.


Observe that I wrote "The power management folks explained". I am not the expert here; I'm repeating what I've heard in the interest of getting information out. Unfortunately, it looks like the the Windows Mobile PC Team Blog has gone dark, so it's not clear to me where you can ask your questions. (There is a more general site on Microsoft and the Environment, however.)

Comments (24)
  1. jMarkP says:

    "…it looks like the the Windows Mobile PC Team Blog has gone dark"

    Pun intended, considering the context of this post? ;)

  2. Falcon says:

    I guessed the power management folks’ answer by the end of the first sentence.

  3. ScottPruitt says:

    This one got me smiling "Oh dear, things are getting pretty bad, you really should wrap things up before I’m forced to stop the car!". Looks like the client got a defective product after all.

  4. Leo Davidson says:

    Same thing happens with user-triggered hibernation and resume, I guess for the same reasons (i.e. the hardware may be lying to the OS about the battery level so it can’t be sure if it’s safe).

    Shame that a few dodgy hardware/firmware implementations can spoil it for the rest of us. Especially as memory has increased a lot which in turn has increased the hibernate/resume times and the niceness of a progress bar.

    When the battery report is accurate it seems like there should never be a need to avoid powering the monitor, unless the user has moved the emergency-resume setting to a really low value.

    Hmm, perhaps I’m not thinking of old, worn-out batteries, though. Maybe all battery hardware becomes unreliable after a while.

    I do so little on my laptop that I keep thinking I should disable most of its memory to speed up hibernation, but I can’t bring myself to "waste" the RAM like that.

  5. someone else says:

    Perhaps that’s another reason why hibernation is disabled with more than 4 GB of RAM …

  6. GregM says:

    To "someone else", I have 8GB of RAM, and I can hibernate (Vista x64 Ultimate).  The follow-up question is "why does the screen go black when the user triggers a hibernation in Vista, rather than showing the progress screen like in XP."  Sometimes my computer will fail to hibernate, and just hangs.  The only thing I can do at that point is forcibly power off.  I can’t tell when this happens except when it takes longer than normal to power off.  Hopefully this has been fixed in Win7.  (I know Raymond isn’t the expert here, and I don’t expect an answer from him.)

  7. someone else says:

    I see, so the restriction is only for NT 5.x. That makes me wonder why …

  8. environment bandit says:

    That’s because Vista is an energy crisis.

  9. Anon says:

    I *never* get a battery low / battery critical warning display or sound in my hp laptop in Vista. Everything is configured correctly, but no warning! Anyone else has this problem as well?

  10. someone says:

    The worse thing is Windows fails to correctly calculate the battery status after a few months, not all of a sudden (so I don’t see how this is a problem with the BIOS, I dunno if this is a fault of current battery technology or how it reports to Windows or how Windows calculates battery life). As a result, this turning-off of the screen begins to happen on my HP laptop at 25% battery level!! In one split second it shows battery level is critical and the next moment it hibernates.

    I also have the same question as many others have asked. Why does the screen go black when you manually hibernate? There’s no emergency situation in that case. That’s because it’s Vista (and poor Windows 7 suffers for inheriting from it) and because it is broken-by-design in many aspects. It’s only that I eventually upgraded to Vista and now Windows 7 because of the OS being overall superior that I’ve begun to see so many design shortcomings and poor decisions in the NT 6.x series? In the days of Windows 2000 and XP, EVERYTHING WAS JUST ABOUT PERFECT. (Okay, maybe not security but everything else).

  11. ::Wendy:: says:

    Like anon,  neither of my current Vista (Home premium and Business edition) laptops deliver a noticable notification low battery warning.

    This is extremely annoying.  Sometimes I take my laptop expecting to be on battery power for 2-3 hours,  and I forget how much time has passed because I’m having such fun with my pc and peers.  YAY!  Then BLACK no warning.  Embaressment.  Public embarressment,  no empathy because colleagues are too sensible to take their PC’s to meetings.

    Hopefully Windows 7 (gotta love the product name) team have worked with battery producers to ensure effective delivery of appropriate warnings.  Or windows has done something more innovative?  

  12. Damit says:

    @someone else / Wendy: Windows 7 might have a new feature which detects when your laptop’s battery is going bad and warns you about it. I don’t know if it works only with LiIon batteries though…

  13. someone else says:


    IIRC you have to (almost) fully discharge Lithium ion batteries from time to time (about once a month) so the internal electronics can correctly calculate the remaining charge.

    An to all: what’s with the your obsession with progress bars? You’ll know when memory is written to disk because *your computer shuts down*!

    Also, hibernation is overrated. I prefer standby. The difference in power consumption is negligible. Especially considering the time it takes to read and write several GB of memory.

  14. Leo Davidson says:

    @someone else:

    The same reason there’s an obsession about progress bars for every other thing in the world. Obviously the operation is complete when the thing stops, but it’s nice to know approximately how much longer you have to wait for that to happen.

    As for hibernation vs standby, the default is to hibernate after a long standby time… I guess you could turn that off and let the battery fully run down instead, but I haven’t. When I know I’m not going to use the laptop for a long time, and thus it’s going to hibernate eventually, I prefer to just hibernate it myself before putting it away.

    That avoids having to worry about something going wrong when it tries to hibernate and the laptop staying powered up when it could be in a drawer without ventilation…

  15. Raymond II says:

    User Data (Saved) > Feedback > All

    Yes, you save battery consumption by disabling the video, but why not start the hibernation process earlier, or if the screen is off, start flashing the Numeric Lock, Caps Lock, and Scroll Lock LEDs in the KITT pattern (Knight Rider ™). That might grab people’s attention. It would work because there’s probably no way to shut off the power to the computer keyboard anyway. The mouse, yes, the computer keyboard, most likely no.

    Feedback is #1 if you’re a user. (User data is implied.)

    [Um, please re-read paragraph 4. Normally, you do get plenty of warning. -Raymond]
  16. Raymond II says:


    Still, I like the KITT idea, but opera rap may have damaged my judgment.

  17. someone else says:

    @Leo Davidson

    “Obviously the operation is complete when the thing stops”

    A bold claim indeed. But progress bars are usually connected to a cancellable operation, so you know if it would be faster to cancel or to finish.

    Of course, the last 2% usually take as much time as the first 98%.

    @Raymond II

    Some computers, especially laptops, do not have Num/Caps/Scroll Lock indicators. However, all of them have a screen.

  18. Stephen Jones says:

    ——"Also, hibernation is overrated. I prefer standby."——

    You evidently don’t live in a country that suffers from power cuts.

  19. someone else says:

    Indeed, I don’t. Stable power for years.

  20. Gregory Kong says:

    The difference between hibernation and standby is between 0 watts of electricty used and [insert non-zero positive number here] watts of electricity used. From a certain perspective, that is either a 100% savings or an infinite percentage increase in energy consumption.

    Myself, I prefer hibernation.

  21. Bryan says:

    There are also substantial differences in how long it takes to resume from Hibernation vs. Standby.  On Windows 7, this seems to be a little better; however, I just turn Hibernation completely off on my desktop.  For whatever reason, if I don’t the system will BSOD if it tries to hibernate when certain applications run.  I imagine this is an app failure, but it’s really hard to pin down.

  22. TJ says:

    I can leave my XP laptop in standby for around a week and when I turn it on, it’ll still have 50% – 60% charge remaining, so I always use standby just because it’ll be back up and running within a couple seconds–plus I have it plugged in probably 99% of the time I use it. Resuming from hibernation, on the other hand, still takes around a minute or so. Also, it fails to recover from hibernation nearly half the time and I end up having to do a hard-reset anyway.

    I don’t know about Vista and Windows 7, never run them on laptops before and so I’ve never dealt with standby/hibernation.

  23. Worf says:

    One thing in Vista I like is the safe sleep – it’ll hibernate, but instead of off, it’ll suspend. Wakeup is fast, but if the battery dies, well, it’ll resume as normal. Like OS X.

    50% charge after suspend for a day means dead after two, which may happen accidentally due to some other emergency.

  24. DWalker says:

    Bah.  I don’t use a laptop (or a cell phone), so I avoid these kinds of problems…  I’m lucky I guess.  Or I planned well.  

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