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100% cpu usage - so why don't numbers under "Processes" column add up to 100%?

On a Win7 Pro 64bit laptop quad-core that's overheating and crashing due to heat & dust (see http://www.experts-exchange.com/Hardware/Laptops_Notebooks/Q_28415779.html) the cpu usage is often showing as 100% in the task manager performance tab, in resource monitor, and in process monitor. But when I look at the processes under the process tab of those programs, and sort so the most usage is on top, they read like, 25, 15, 10, 5, then nothing. They don't seem to add to 100%. Why would this be? Does it relate to quad-cores?

Also, this computer can be very slow when RAM, Network, and Disk usage show as very low, and CPU usage shows as 50-80% only. Could this be explained by the overheating?

Thx!
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dgrrr
Asked:
dgrrr
3 Solutions
 
Dan CraciunIT ConsultantCommented:
Click on "Show all processes" and you will see all that is running.

Also, I recommend Process Explorer. Way better than Task Manager.

HTH,
Dan
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PerarduaadastraCommented:
50-80% CPU usage is abnormally high unless you are intentionally running single or multiple CPU-intensive programs. A faulty process would normally show in Task Manager, but a malicious process can conceal itself from that utility.

Dan Craciun's suggested tool is more likely to reveal a malicious hidden process than the Windows offering. I can confirm from my own experience that Process Explorer is indeed excellent.

In regard to the overheating CPU, the most reliable method of ensuring that the processor heat sink is not blocked is to take it out of the machine and physically check that it's free of dust and fluff. Many times I've found that a CPU fan exhaust vent that looks clear is in fact clogged with material that's been sucked in by the fan.
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akahanCommented:
The processor will slow itself if it is overheating.  When it does, even very simple tasks will run extremely slowly, and processor utilization will be abnormally high.

Assuming you're running an Intel processor, it's very easy to see if it's doing that.

Install (free) Intel Processor ID utility, from here:  

http://www.intel.com/support/processors/tools/piu/sb/cs-014921.htm

Run it.  It will show you "expected" and "reported" speeds for your processor and system bus.  If "expected" is higher than "reported," then the processor is slowing itself down, typically due to overheating.  Solution is nearly always to blast compressed air in the intake and exhaust areas and around the processor, and make sure fans are operating correctly.
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