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In the attached screenshot, why does it show that I have four CPUs when I know I only have a single CPU installed on my PC? What do each of them refer to?

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What CPU do you have? –  David Schwartz Mar 10 '12 at 8:14
    
@David Schwartz - I believe it is a Intel Core i3 330M –  PeanutsMonkey Mar 10 '12 at 8:18
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Its referring to seperate CPU cores.

You only have one CPU installed in your system, but it might be a quad-core, or a dual-core with hyperthreading.

EDIT: An i3-330M is a dual core CPU with hyperthreading, so in this specific scenario, CPU1 and CPU2 are the first core, CPU3 and CPU4 are the second core.

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Thanks. I can see that CPU 2 and CPU 3 are bearing most of the brunt. How can I relate this to the process (application or services) that is utilizing the CPU? –  PeanutsMonkey Mar 10 '12 at 8:14
    
@PeanutsMonkey You can go to the processes tab to see which applications and services are using the CPU. Which CPU cores end up taking the load is usually fairly random, and there's nothing special in CPU2 and CPU3 being under load while CPU1 and CPU4 do nothing. –  William Lawn Stewart Mar 10 '12 at 8:23
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The OS scheduler will try to load virtual cores that don't share a physical core if it can. This makes better use of available cache and execution units. So it's not unusual, during light load, to find two cores with the majority of the load and two cores nearly idle. –  David Schwartz Mar 10 '12 at 8:26
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@PeanutsMonkey Processes can run on more than one core at a time, or switch which cores they're using. As far as I know there is no method to find out which applications happen to be running on which cores. You can limit them to specific cores, but you can't see which cores they're using at any given time. –  William Lawn Stewart Mar 10 '12 at 8:52
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@PeanutsMonkey "Hyperthreading" means that each physical core has more than one virtual core. In your case, each physical core has two virtual cores, so four virtual cores total. You can't really tell which CPU core is assigned to which process because the scheduler deals with tiny fractions of a second -- by the time you got that information, it would be obsolete. Why do you care? What's your actual problem? –  David Schwartz Mar 10 '12 at 9:00
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Your Core i3 330M has two physical cores, each of which provides two virtual cores to the operating system. So your single physical CPU looks like four CPUs to the operating system.

Be aware that your CPU's total processing capability is not fixed. While you don't have Turbo Boost, you do have EIST (Speed Step). Percentages are always a percent of the currently available CPU power at the current multiplier, not the total performance of the CPU at its maximum or normal multiplier.

In your case, the maximum and normal multipliers are the same. So as long as the CPU isn't very lightly loaded, the percentages should be of maximum.

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Thanks. I'll need to dig deeper to understand what you just answered as it just went past my head. All I understood what that my CPU has 2 cores which provides 2 virtual cores hence the operating system displaying 4 CPus. What I did not understand was Be aware that your CPU's total processing capability is not fixed. What do you mean by that? –  PeanutsMonkey Mar 10 '12 at 8:44
    
@PeanutsMonkey He means that CPUs can slow down or speed up (to conserve power, or process tasks quicker, and so on), so 50% CPU usage doesn't necessarily mean 50% of the maximum speed of the CPU. 50% CPU usage now might not be the same as 50% CPU usage 5 seconds later. –  William Lawn Stewart Mar 10 '12 at 8:50
    
@William Lawn Stewart - Sorry for being such a n00b but what do you mean by 50% CPU usage doesn't necessarily mean 50% of the maximum speed of the CPU. 50% CPU usage now might not be the same as 50% CPU usage 5 seconds later Do you mean that assuming that the maximum speed (not sure if you mean in Ghz for example) is say 100 50% CPU usage does not mean 50% of 100. Is that right? If so what does 50% CPU usage refer to then? –  PeanutsMonkey Mar 10 '12 at 9:01
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50% CPU usage means the CPU is in use 50% of the time. However, the CPU can reduce its clock speed if the load is low. So 50% could still mean very low load or it could mean half load. It just can't mean heavy load. (In practice though, your particular CPU will run at full speed unless it's very lightly loaded, assuming you don't change the power management settings from their defaults. This is because your CPU doesn't have turbo boost.) –  David Schwartz Mar 10 '12 at 9:05
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