How do I find out what program is using all my CPU?

All evidence to the contrary, computers can really only do one thing at a time. OK, a dual-core or dual-processor machine can do exactly two things at a time, a quad core can do four, and so on. But a single CPU can do exactly only one thing at a time. It just switches between them all really, really quickly.

So, when one program needs all of the CPU's attention, other programs that need the CPU might not get enough time to do their work. That typically results in a very slow system from a user's perspective.

We can use Task Manager to figure out who the culprit is, but I very much prefer the free download Process Explorer. Download and run it, and you should see something very much like this:

The default display shows all of the tasks running on your computer, in hierarchical order; if program A was the one that started program B, then program B appears indented beneath program A. That can be helpful for other reasons, but not what we want here.

Click the column labeled CPU and Process Explorer will sort the processes by CPU usage. The processes using the most CPU will be listed at the top:

Here, you can see that when I took this image, my CPU was actually 68% idle; in other words, it was doing nothing at all two thirds of the time. The next highest program on the list was SnagIt, the screen capture program that I use, using about 14% of CPU, followed by Windows Explorer, Trillian, and others in decreasing order.

Here's another example after starting up an audio processing utility:

Here, that program is using about 50% of my CPU's available processing power.

In many reports that I get, it's a program called "svchost.exe" that has people concerned and mystified. I've talked about svchost and why there might be more than one copy running on your machine before. As of this writing, there's a common problem that people are experiencing involving the Windows Update service causing its instance of svchost to use all available CPU. If you right-click on the svchost that appears at the top of Process Explorer's CPU usage list, click Properties, and then click the Services tab, you'll see all of the system services that instance of svchost is providing:

You'll see that this is the instance of svchost that handles Automatic Updates on my machine and that I have the option of stopping that service right there.

Regardless of what's actually causing your CPU usage problems, if you're having any, Process Explorer is a quick way to not only identify the culprit, but as its name implies, explore some of the interesting information about the processes running on your machine.