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In Windows Task Manager the Performance tab shows the first CPU maxed out, the other 7 just idling along with the occasional spike. What gives?

More info: I've got 8GB and only 4.5GB are being used. The Processes tab has no indication of any process hogging processing power. In fact System Idle Process is 98-99.

When I program stuff and have like 8 to 12 applications going (several directly unrelated to programming of course) my computer slows to a crawl.

System Info:

Intel Core i7-2600K Processor (quad-core with hyper-threading), 
8GB RAM, 
Intel BOXDZ68BC LGA 1155 Motherboard, 
500GB HDD
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    Are you running a single, slow process? Many processes simply aren't programmed to use multiple cores. Try running Prime95 briefly to see if it uses all of your cores
    – Ben Brocka
    Nov 3, 2012 at 15:26
  • I ran Prime95 as you suggested and it maxed all 8 CPUs. (I know there is only 4 cores, but with hyper-threading Windows reports 8 CPUs in Windows Task Manager, so that's what I am referring to.) I was running one program that could have been the culprit, but it usually does not run so slow, nor does it slow other programs. So maybe it was a combo of processes, but why did they not run on separate cores?
    – revloc02
    Nov 3, 2012 at 15:36
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    if Prime95 maxes out the cores, then it's working right. Have you ruled out HDD and memory bottlenecks? Nov 3, 2012 at 16:00
  • Task Manager adds interrupt processing time to System Idle Process. If System Idle Process is 99% but one core is 100%, it is maybe processing interrupts. Use Resource Monitor, which breaks out interrupts and DPCs. (I assume this is Windows 7) Nov 3, 2012 at 16:07

3 Answers 3

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Many apps don't use all cores. They aren't programmed for it. Then they will use one core and will overload it.

But you can tell Windows to run that process on 2,3, ... and in all cores.

For doing it, follow these steps:

  1. Open Task Manager
  2. Select tab Processes
  3. Right click and select 'Set Affinity'
  4. Select on which cores you want to run process.
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    You can tell Windows to use which "threads" it can use doesn't mean the program will actually USE them in the traditional sense.
    – Ramhound
    Nov 3, 2012 at 16:40
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    @Ramhound , you're right, but this makes better performance for a lot of programs;)
    – Searush
    Nov 3, 2012 at 16:58
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your processor is quad core it will run 8 threads on multithreading however not all applications are programmed to use multiple threads some applications just require 3 threads so it means that application will use only one core or two. so even on setting the affnity of process for 4 cores it will still use less hardware

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If you have Intel Core i7 2600 CPU first check if it is Dual Core or Quad Core.
Some high end Core i7 CPUs are 6 core processors , and the other cores you see in Task Manager performance tab are virtual cores.

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    It is a quad-core CPU with hyper-threading. So 4 cores, but Windows reports 8. Still it seems like only one core was running the hard stuff, and everything (all programs) was bogging down.
    – revloc02
    Nov 3, 2012 at 15:42
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    @raven, you could edit your first answer, and add there your second answer;)
    – Searush
    Nov 3, 2012 at 16:59
  • @revloc02 - Unless you give exact details of what processes were running, and how many threads, each process was using your conclusion is incomplete. It sounds like you were just using process intensive applications.
    – Ramhound
    Nov 3, 2012 at 21:38

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