Helping people with computers... one answer at a time.

Mysterious CPU usage in the middle of the night isn't all that mysterious. There are a number of things that are automatically configured to run when you might be sleeping.

I have an ALIENWARE M17x Intel(R) Core(TM) i7 CPU Laptop with Windows7 Ultimate SP1, I use this computer almost 18 hrs a day. My weird problem is that almost between 12 to 2 o'clock in the morning, the system slows down rapidly and sometimes it hangs up. It seems like it's loading the CPU because the CPU usage meter reads almost 96%. This condition happens almost every day. Although only Yahoo or Skype are open. I really don't know why it happens. I would appreciate any thoughts you might have.

In this excerpt from Answercast #38, I look at a high CPU usage in the middle of the night that, honestly, doesn't surprise me.

Late night slow-down

Yea, I've got a couple of thoughts actually.

  • One: to avoid any guessing, I would go out and get a copy of Process Explorer, the free process management tool you can get from Sysinternals and have that running.

I mean, a few minutes before midnight, fire that thing up. Have the display sorted by CPU usage (you can see how to do that in my article, "How do I find out who's hogging all the CPU?")

That will show you in real time which applications or which files are actually using all of the CPU. You can then immediately identify who it is that's slowing your machine down so dramatically.

Late night malware scans

Now, without that information even, I still have a couple of really good guesses.

Between midnight and two o'clock in the morning. I'm willing to bet that:

  • Your anti-malware tools are starting up a scan;

  • And/or Windows is automatically firing up a defrag of the hard disk;

  • Or some other task that Windows plans to do for maintenance is scheduled to start up automatically between midnight and two o'clock in the morning.

Task manager

The easiest way, honestly, to find out exactly what's happening is using Process Explorer, like I explained a moment ago.

But if you're really curious, you could go into the Task Manager.

If you take a look at Control Panel, you'll find that there's an Administrative tools section and there is the Task Scheduler.

If you poke around in there a little bit, I'll think you'll find that there are a number of scheduled tasks that Windows has prepared for you.

  • My guess is that you will find your anti-malware tools there as well.

  • Perhaps your backup program, if you're running one.

  • Perhaps Windows own defragger, or other maintenance utility, is firing up automatically as well.

If those turn out to be the problem, then you have a couple of options.

Manage the schedule

The biggest option you have is to:

  • Simply change the schedule at which those things are happening.

  • Stagger them a little bit better so that they're not all trying to start at once.

  • Or if they have options to be run in a less impactful way (as some of the anti-malware tools often do), change the way that they're configured to run.

All of it depends on exactly what it is that's firing up between twelve and two. And like I said, Process Explorer is the way to find out what it is: since you happen to be awake and at the computer during the time it's happening.

Article C5627 - July 27, 2012 « »

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?

Ken B
July 27, 2012 10:04 AM

Without anything else to go on, I agree it's probably a scanner/defragger set to run at midnight. (Given the CPU spike, it's probably not a defragger, which in my experience is disk I/O bound.) However, note that things like malware scans probably won't be in the task scheduler. Often, the program is running all the time, and is configured internally to start a scan at a certain time. So don't be surprised if you don't find anything in the task scheduler to explain the timing.

Follow Leo's advice -- get Process Explorer. I have it running all the time, since it takes very little CPU when minimized. It's also useful for finding out what program is eating up memory, not just CPU.

Chris Roberts
July 27, 2012 3:09 PM

Hi, my computer slows down in the early hours too, so I installed Process Explorer as you suggested.
The problem is, I don't know what the readings mean or how to reduce CPU usage! You suggest changing or staggering processes.... I don't know where or how to do that either! Can you recommend a link to help with my inadequacies?
Thanks - love your newsletters!

This article will show you how to use process explorer to identify the top CPU users. What you do next depends on what they are: How do I find out what program is using all my CPU?

Comments on this entry are closed.

If you have a question, start by using the search box up at the top of the page - there's a very good chance that your question has already been answered on Ask Leo!.

If you don't find your answer, head out to to ask your question.