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What is it that Windows is doing when it shuts down?

Assuming I've saved everything, what negative impact does powering down instead of shutting down properly have? We've all done it at some point and personally I don't know anyone whose machine has died as a result.

(Just to be clear, I know I shouldn't, I'm just not sure why.)

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10 Answers

up vote 39 down vote accepted

It's unlikely that the whole machine will die, but if there's anything still in file write buffers, you'll lose that data... and basically the machine probably won't know the difference between you powering it off and it shutting down due to a power cut.

Services won't get the chance to shut themselves down cleanly. For instance, if you're running a web server, when it gets asked to shut down it may well complete any existing requests (with a timeout) rather than the connection just going away.

The "file write buffer" doesn't just have to be the Windows buffer, either. Again taking a web server example, the logging might be buffered so it only writes to disk every 100 requests or something similar. A clean shutdown will flush this appropriately; a hard shutdown won't.

If you have online services, a clean shutdown may sign you out of them appropriately, instead of the service thinking you could just have network problems.

Basically think of anything a system might want to do when closing down in terms of either the on-board disks or connections to other systems (such as network connections) - all of those are going to be happier when shut down properly.

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Jon Skeet has already made all the critical points from a software and OS standpoint.

I have just one small point to add that might possibly be of significance.

Shutting down the computer where the motherboard chip-set comfortably powers down the system is different from a sudden power cut to the system.

At the minimum this could damage your power supply unit (the thing usually behind the rear power-switch on your CPU box). In a worse case, the motherboard power regulator devices may breakdown. That is a motherboard replacement cue usually. And, there are worst cases.

If you have an emergency, at least get to a standby or shutdown state with a depressed power button -- takes not more than 3-5 seconds -- before you cut power.

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It really shouldn't damage the PSU or motherboard, at least not unless you're doing this a lot (i.e., it may put a little bit of stress on them). It also puts stress on the hard drive, as it has to do an emergency head park. –  derobert Jul 18 '09 at 6:41
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@derobert, to my best electronics understanding, there is always a probability of failure. With multiple tries on cutting power, you are just increasing that probability. –  nik Jul 18 '09 at 7:45
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I wouldn't expect it to do any more harm than pulling out a USB drive without ejecting it - usually fine but could do damage if it's quietly doing something important when you switch it off. I suppose it depends on how much you dislike reinstalling if it does break it :)

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As with pulling USB sticks out of a machine without Safely removing them first, when I'm asked this question by family or work colleagues I say that is probably won't be a problem if you accidentally do it occasionally, but don't get into the habit of it as the risk is small but a definite possibility. I've certainly seen enough corrupted drives over the years.

Oh, and I usually add "Don't come crying to me if you ignore this advice and your hard drive/memory stick ends up corrupted". *8')

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In addition to all the answers above, on the machine that have a RAID on their HDD and a high IO activity, a hard poweroff will most likely interrupt HDD IO required for the RAID to function sometimes leading to HDD failure and frequently - to random data loss.

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Yes, that could happen if the RAID controller does not have a battery backed buffer which would keep unfinished writes until the main power is restored. –  pabouk Nov 18 '13 at 14:25
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I found an article that makes it sound like it's not such a big deal, just that you may run into some very small issues if it was writing data to the disk or using other I/O. That shouldn't be much of a problem since you've already saved everything — though you should close programs as well. Still, a proper shutdown is probably the best way to go if you have the choice.

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You may have saved everything, but it doesn't mean your OS has. The OS is constantly doing things in background that you are not aware of... you could have trouble if you stop something mid-flow. (Less likely these days, but still possible) –  CJM Jan 26 '11 at 12:03
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There could be disk activity happening in the background that you're not aware of. You could end up with corrupted files. I'm not saying you will but it increases the chances.

Examples of things that could be happening even when you think the machine is idle:

  • Defragmentation
  • Windows Updates
  • Other software updates e.g. virus definitions
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What I could find:

In my experience, it has never physically hurt my computer by manually turning off my computer. The only thing you have to be concerned about is what type of programs are running at the time your shutting it down. If you do a force shutdown via holding the power button down, programs that are running won't save any current data that they have. So lets say your running something that keeps logs and only saves the logs when the program is terminated. When you do a force shutdown, those logs won't be saved.

I'm not positive about information not saving when you press the power button, like if your computer is running fine and you press the button. So correct me if I'm wrong. But I know for sure that when you hold the power button in for the 3-4 seconds, nothing saves.... especially when your computer is frozen.

I normally don't dare to take any risks, but that might be some "legacy" habit from when such things were a problem. If anybody more technical can explain WHY it's not a problem that would be awesome.

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As for "legacy habits", before ATX the way to shut down a PC was to cut power at the power supply. ATX changed this to electronically controlled through firmware or software, which among other things allows the operating system to power off the computer (as opposed to simply putting the computer in a state where it can safely be powered off). –  Michael Kjörling Sep 12 '13 at 11:13
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Assuming you've saved everything, no damage. I do it all the time and I have yet to see even one problem. It's probably NTFS journaling saving me.

I do remember exercising more caution with Windows 98 (FAT, of course), but even then all I get is a scandisk on boot. I think it's a legacy habit. I'm guessing most of the other typical precautions are just Microsoft disclaimers.

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I'm not sure if it's a problem anymore, but I recall that back in the day (15 years ago when win95 was being released) there was a risk that hdd read heads, if reading, could shift when the power was cut and scratch the disk. I suspect the emergency head park that derobert mentions was the resolution to that.

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