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We're all told to shut down Windows before turning power off, but what if the power just goes out? If you're not protected, bad things can happen.

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 issue.

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 out 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 very rare cases I can think of scenarios where hardware might be damaged. What comes to mind are perhaps attached USB flash drives that also need the equivalent of a "safely remove hardware" on shutdown. If they don't get that, then perhaps a poorly designed device could be damaged.

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

So 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.

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

A great example is a windstorm we suffered here in the Seattle area late last year. As trees fell onto power lines various things would happen:

  • Power would "blink" while the power grid automatically re-routed our power through other circuits, compensating for a supply line that had just broken.

  • Power would "brown out" as power lines began to short or fall onto trees and other structures where they made a partial connection. Brown outs are situations where voltage on the line falls levels much lower than the normal 120 volts we use here in the U.S..

  • Power would "surge" as power lines shorted with each other or fell 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.

"All of your desktops, most printers and other equipment should be connected to power though a surge protector."

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, though, since the primary high-voltage feeds that bring power into your area are still typically above ground. And of course there are certainly other situations besides windstorms that can cause power failures with all the symptoms that I've described above.

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

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

Some equipment can handle that mess.

Some equipment cannot.

In fact, a lone power surge can certainly 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 turn off power in the case of a power surge.

  • Uninterruptible Power Supplies UPS's are usually large batteries with the appropriate circuitry to continue to provide backup power if the primary power source fails. A side effect is that they also typically include power "conditioning" which can eliminate temporary drops, surges and brownouts, and in the worse case will 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 though 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 would make a lot of sense.

Laptops and equipment that use power "bricks" which 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 only 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 on-line for a few hours before the battery runs out.

Article C3148 - September 13, 2007 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

Not what you needed?

September 13, 2007 9:53 PM

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.

S Deepak
September 14, 2007 9:30 PM

Sir your are not only giving suggestion but helping a lot to improve my power of knowledge thank you sir

September 15, 2007 11:06 AM

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!

September 15, 2007 11:48 AM

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.

September 16, 2007 4:16 PM

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..

Leo A. Notenboom
September 17, 2007 9:07 AM

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)


Brad L.
September 21, 2007 3:37 PM

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! ;)

September 24, 2007 12:59 PM

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 !!!

October 5, 2007 8:00 PM

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.

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