Can CPU temperature cause the CPU to appear to spike to 100% in Task Manager?

Question

I've been having a long running issue with my CPU spiking while watching Netflix. After going through all the hardware/ software troubleshooting I can think of it looks like this is issue is related to the temperature of the CPU itself.

It's a Windows 7 machine with minimal software installed running Chrome/Silverlight to watch Netflix.

What Happens - CPU usage sits at 10-30% while watching Netflix. Occasionally the video will stutter, the audio will continue for a few seconds, and then the video will move very quickly and "catch-up" to the audio. During this time the CPU usage displayed in Task Manager/ Resource Monitor will jump to 100%, with Chrome being attributed to the increase.

I discovered the more I cool the CPU - i.e. take the lid off the case, put the PC in a cooler location - the less likely this is to happen.

Running HWMonitor it seems that the apparent spiking is more likely to happen the closer the CPU temperature is to 60C - the CPU is a AMD Athlon 64 X2 Dual Core Processor 6400+ 3.2Ghz.

The Problem - is the CPU heating up because it's running at 100%, or is the CPU appearing to run at 100% because it is overheating? The demonstrably effect cooling the CPU has suggests it's the later.

My Question - How would Task Manager react to an overheating CPU? Could the 100% reading be showing CPU throttling (i.e. showing the CPU using 100% of available resource)? Or would CPU throttling result in the Task Manager showing the percent the CPU is throttled to?

For example if CPU throttling to 20% kicked in due to overheating while the CPU is at 30% should the Task Manager show 100% or 20%?

Answer 1

Task Manager shows how busy the CPU is. This is unrelated to the "maximum" performance of the CPU. So if you are using 80% of the CPU at a normal performance level, and the CPU clocks back to 50% performance (possibly due to temperature, in your case), the Task Manager should show 100%. The processes want 80% of full performance, but they only have half of the full performance, so they will use 100% of what is available. Task Manager will show 100% because the CPU is 100% busy (but at a lower performance level).

So in your example, if CPU throttles back to 20% performance when usage is 30%, Task Manager will show 100%.