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If Shutting Down Windows Cleanly Is So Important, What Happens When the Power Just Goes Out?

Question: I am aware that not going through the proper Windows shutdown can possibly have negative effects on a computer. But my question is if a computer loses power (due to a household power outage, not anything wrong with the power supply), are these negative effects strictly software related (meaning a format and reinstall would fix them), or might it cause hardware problems as well?

Shutting down Windows properly before turning off the power to your computer is important.

Not doing so can result in data loss and corruption as files are left only partially written to disk. But just turning off the switch is unlikely to actually harm your hardware.

Surprisingly, a household or other area-wide power outage turns out to be a completely different, riskier issue.

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As I said, shutting down Windows properly before turning your computer off is important.

Windows often keeps things in memory (RAM) that you really want to have written to disk, and shutting down Windows gives it the opportunity to flush all that information to the hard drive. In addition, if you happen to turn off the power while Windows is writing something to the disk, you run the risk of corrupting files. In the simplest case, you may never notice. In the worst case, your system might become unbootable.

In extremely rare scenarios, hardware might be damaged by just turning off the power. USB flash drives, for instance, really need the equivalent of a “safely remove hardware” on shutdown. If they don’t get that, a poorly designed device could be damaged. I would hope that most are more resilient than that.

But actual hardware damage from turning off the power switch at the wrong time is extremely rare. More common are data-related errors, which, as you say, can be resolved in the absolute worst case with a format and reinstall.

Power loss

Uninterruptible Power SupplySo why is household power loss different?

Well, to be fair, many times it’s not. Power just … goes out, as if someone threw a switch. That’s pretty close to turning off the power as we discussed above.

Unfortunately, all too many times it’s nowhere near that clean.

A great example are windstorms we suffer in the Seattle area from time to time. As trees fall onto power lines, various things happen:

  • Power “blinks” while the power grid automatically re-routes our power through other circuits, compensating for a supply line that has just broken.
  • Power “browns out” as power lines begin to short or fall onto trees and other structures, where they make a partial connection. Brown-outs occur when voltage on the line falls to levels lower than the normal 120 volts we use here in the U.S.
  • Power “surges” as power lines short with each other or fall onto other electrical equipment. A surge pushes the voltage above the normal 120 volts. Automated equipment is supposed to cut power when this happens, but the leading edge of the surge almost always makes it out to customers in some form.
  • After any of the above, power may finally go out. It may go out suddenly, it may brown-out and go away, or it may go away in a sudden surge followed by darkness.

I use trees and a windstorm as an example here, since in our area most of the power distribution network to homes and businesses is above ground due to the distances involved. Even areas with primarily underground power distribution are still at risk, since the high-voltage feeds that bring power into your area are still typically above ground. And, of course, certainly other situations besides windstorms can cause power failures with all the symptoms I’ve described above.

Losing power due to a power outage is typically not nearly as “clean” as just turning off a switch.

Power loss protection

Consider your poor computer (or any electronic device) connected to power that’s browning out, surging, blinking, and more before it finally goes dark.

Some equipment can handle that mess.

Some equipment cannot.

In fact, a lone power surge can damage sensitive or just plain cheap equipment.

So, what do you do?

I have two recommendations, depending on how frequently you experience power problems in your location.

  • Surge protectors. Note that a “power strip” is not necessarily a surge protector. A power strip merely distributes power to multiple outlets, while a surge protector includes additional circuitry to automatically and cleanly cut power in the case of a power surge.
  • Uninterruptible power supplies. UPSs are usually large batteries with the circuitry to continue to provide backup power if the primary power source fails. As a side effect, they typically include power “conditioning”, which can eliminate temporary drops, surges, and brownouts. In the worse case they simply switch to battery backup if the incoming power becomes too unstable.

What you need depends on your situation. Sort of.

There’s no reason not to use a surge protector. They’re inexpensive insurance. All of your desktops, most printers, and other equipment should be connected to power through a surge protector.

If you experience frequent power problems, or if your computer is particularly sensitive or critical, then getting a UPS and connecting through that makes a lot of sense.

Laptops and equipment that use power “bricks” that convert from household voltage to something lower typically don’t need any special treatment. Connecting through a surge protector doesn’t hurt. Connecting a laptop (which in a sense has its own form of “battery backup”) through a UPS is somewhat pointless, and would add an unnecessary drain on the UPS’s battery if the power went out.

In my case, my computers are connected through surge protectors, and a subset of my networking equipment is connected to a UPS. My laptops, of course, will run on their internal batteries in case of a power failure. I simply make sure that the modem, router, and wireless access point all have backup power from the UPS. This allows me to stay online for a few hours before the battery runs out.

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14 comments on “If Shutting Down Windows Cleanly Is So Important, What Happens When the Power Just Goes Out?”

  1. While living in Florida a few years ago, I made friends with a fellow who worked as a manager at the local power company. He told me that many computer users have a surge protector, but aren’t aware of the danger brown-outs can cause their electronics – including computers, TVs, and other expensive gear. It seems that most of the interfaces in modern electronics (the power supply) will attempt to keep the flow of electricity to the rest of the device at a steady state. If the incoming voltage begins to drop, the power supply will try to adapt; if the incoming power gets to brown-out conditions, the power supply may work so hard that it destroys itself in the process of trying to keep the proper power flowing within the device. Even a $50 Uninterruptible Power Supply (UPS) will stop brown-out damage.

  2. Fortunately, here in the UK, we don`t get too much in the way of serious power cuts, but I`m located rurally and if there`s a storm, the power does sometimes take a dive. Being an ex-telephone engineer, I`m fairly aware of the problems that can arise, especially in the situation where low volts is worse than no volts at all. This happened in the last cut we had for 16 hours and we had about 50 – odd volts coming through (normal UK is 240)and various pieces of my electronics gear over and above my PC`s, (hi-fi amp, etc) were initially trying to run, cutting in and out and doing odd things! I`d already turned everything off before being advised to do so by the electricity supplier when I reported the problem. This is slightly off-topic, but, as I understand it, motor-driven appliances (fridges/freezers, etc.) can sit there trying to run in a low-volts situation and can actually cook up if they are not running properly, as some motors/compressors have built-in fans to keep them cool. If these aren`t running properly you could end up forking out for a new one! Don`t do what I did (I feel silly here) and forget to turn said freezer back on after power is restored! No further comment!

  3. You said that connecting a laptop to a UPS is pointless but since we’re told NOT to leave the battery in while connected to an electrical outlet then if there is a power failure wouldn’t the machine still be vulnerable to all the nasty things that can happen from not being shut down properly? If a UPS is not the way to go then what is? My laptop (and printer, scanner etc) is currently connected to a good surge protector. When the voltage fluctuates I hear a “clicking” sound and see the “boost” or “trim” light go on.

  4. Not to leave the batter in while connected to an electrical outlet? How else would you recharge the battery then? The battery on your laptop will act exactly the same as a UPS…. If the power goes out, your battery will take over.. Notice you can freely attach and detach the power from your laptop without worrying or losing any kind of current form the computer… You can do the same with a UPS..

    Hash: SHA1

    I know that there are many who recommend removing the battery from your laptop
    if you’re going to leave it plugged in for a long time. (After letting the
    battery recharge, of course.) Supposedly it lengthens the life of the battery.

    I don’t do that. For various reasons, the batteries are in all the time on all
    four of the laptops here. The battery acts as a UPS, particularly when the
    power cord gets tripped over, or you want to move the laptop from one location
    to another. A quote from an earlier article of mine:

    “A concern that I’ve had for a long time is whether or not leaving a laptop
    plugged in for extended periods of time would harm the battery. Today’s designs
    pretty much expect that type of usage, so it’s not the issue I was afraid it
    might be.” – from

    But yes, if you do remove your battery, then you’ll want to treat your laptop
    as if it were a desktop, and plug it into a UPS.


    Version: GnuPG v1.4.7 (MingW32)


  6. Re: ‘..while a surge protector includes additional circuitry to automatically and cleanly turn off power in the case of a power surge.

    Granted, not all power strip appearing devices (multiple outlets) are surge protectors. Of the units that ARE surge protectors, many of them are useless! Why? Because after whatever protection in them has been ‘used’ and therefore NO protection exists at all, they STILL PASS POWER TO THE OUTLETS. They do NOT, ‘..cleanly turn off power..’

    You think you are protected when you are not.

    A surge protector/expansion strip device that works as it should will NOT pass power once the suppression/protection part of it is ‘used’ (damaged due to spike suppression). The simple ‘damaged but still useable’ devices would likely consist simply of MOVs (Metallic Oxide Varistors), avalanche or zener diodes.

    I think! ;)

  7. hi, you said “In the worse case your system might become unbootable.”

    well, this happened to my boyfriends computer. Basically, whenever the computer was turned on, it would freeze while booting up and none of the safety modes would work.

    We fixed this problem by using a XP restore cd however when we finally go to the start up menu we realised that all his pictures/music/most of his programs had disappeared.
    Yet, when we looked at the memory the computer was still taking up as much memory as it used to which we took to mean as the files are still on the computer.

    Is there anyone out there who could help me on getting these files back?

    Does anyone know of any programs that could do this for me?

    We are not sure where the files could be, we’ve looked everywhere on the hard drive.
    We’ve used some file recovery programs but because the files aren’t techniqually ‘deleted’ as such, those programs are virtually useless to us.

    Please help !!!

  8. Thanks for the feedback. I feel better now about leaving the battery in all the time and not just when it’s charging. Surges, brownouts and total power failure, while not regular, are not uncommon where I am. I use my laptop many hours everyday so it’s good to know I have the option to let my battery function like a UPS.

    One more question. How do you know if your surge protector is actually working? According to the post by Brad L we may think they’re working when they’re not. I use a Tripp Lite voltage regulator and conditioner and would really like to know for sure that it’s working. Is there a way to find out? It shows a steady green light most of the time but occasionally the boost or trim light would go on accompanied by a “ticking” noise. Any feedback would be appreciated.

  9. A modestly priced UPS is a good investment to protect your costly computer equipment from power drops, brownouts, spikes, and surges. I have one each for both desktops, my SAT receiver-DVD, and a pair of modems for internet and a VOIP phone system. Those on the computers have an endurance of just several minutes and so are arranged to send them a shutdown signal (easy to set up). Peace of mind for our tech-dependent era.

    Regarding the laptop battery, by all means keep it in. But do use battery management software (standard on some higher quality gear) to extend battery life. Lithium-ion batteries have longest life at approximately 50% charge so, unless I expect to use it on battery for more than 2-3 hours, I have the laptop set to stop charging at 55%. And if you ever have to replace your laptop’s battery get the OEM part for safety reasons (more likely to be a quality part and matched to the charger’s characteristics).

  10. I used to use UPSes with a few 120Ah batteries. So when the power got down (regularly), we still had electricity for eight hours.

  11. Is there anyone out there who investigates instances of paranormal computer activity? Of all the crazy things I have saw PC’s do over the years, last night my computer done something that nearly has me questioning my sanity. Here is what happened.

    I never turn my computer off at night and it often will be running consistently for a week or two at a time until I reset it, due to instability or a software upgrade that requires a restart. Or if the power goes off; this obviously causes as reset. This computer does not have an Uninterruptible power supply (battery backup) even though I know I probably should. So a power outage ALWAYS results in a computer reset, or so I though. Last night at around 10 pm soon after I was in bed we experienced a whole house power outage that lasted approx. 3 minutes before power was restored. Everyone in the house agrees on the time, duration and the fact that it affected the entire house. There were multiple items in my room that lost power. This was not a “brown out” where the light go dim for a few seconds and then resumes. It was a complete black out.

    When I got to my computer this morning I fully expected my computer to appear as it would have been after a fresh power start. By now you probably all know where this is going… Yes, to my surprise the programs that I had left open the night before when I left it about 9pm where all still running and the data files were still open! My password did not need to be entered as it normally would after a reboot. My computer had clearly remained running with no power. Just to be sure, I opened up the task manager which shows how long it has been running uninterrupted, and it showed 14 hrs. This put the time of the last restart at about 7pm last evening and I clearly remember having reset it at that time because of an instability issue.

    The only theory I have at this point, and this is pretty far-fetched, is this: I had my wheelchair charging in an outlet on the same circuit breaker just a few outlets away. I normally don’t charge from here, but it was tonight. Possibly though some crazy electrical abnormality the wheelchair batteries acted as Uninterruptible power supply (battery backup). I don’t understand electricity enough to know whether this is a possibility, but I understand computers well enough to know that they cannot remain running without electricity.

    Anyone have any other theory?


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