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I've seen this behavior in MacOS's Activity Monitor as well.

Here's a picture of an example: Playing Minecraft with OpenJDK. I frequently see over 100 CPU when the game's abusing the system. My girlfriend's MacOS has reported over 100 percent as well on her own programs (not just minecraft).

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I am not certain about this, but maybe the program is running with multiple threads (parallel) and the reporting does not know this -- causing accounting errors...? –  nik May 3 '11 at 16:43
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where do you you see more than 100% cpu, a screenshot would be useful. –  Cas May 3 '11 at 17:14

4 Answers 4

up vote 12 down vote accepted

100% CPU usage represents full usage of one CPU core.

Anything above 100% represents a multithreaded process utilizing more than one core.

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Banking from this answer, would a process using both cores full-power show 200% utilization? –  user6658 May 3 '11 at 18:53
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Yes, but I've never personally seen it done. Most multithreaded apps (that I've seen anyway) have a heavy thread taking a lot of CPU time, and another thread or thread group handling the easy stuff. –  axon May 3 '11 at 21:45
    
Yes, I've done it. In fact I've managed to max a quad core before. –  Elder Geek May 6 at 14:55

There are 2 ways to show the CPU usage. In the preference dialog you can choose to between these modes.

The default is IRIX mode which can show a CPU usage of more than 100% on machines with more than 1 logical CPU[1]. More specifically, the maximum CPU usage can be ((# logical CPUs) * 100)%.

In Solaris mode the maximum CPU usage is 100%. Basically this takes the IRIX mode value and divides it by the number of logical CPUs.

This is all consistent with the the top command line tool so see the top man page for more info. http://linux.die.net/man/1/top

[1] If a processor supports hyper-threading then each core can appear as 2 logical CPUs.

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It means you are utilizing the full power of CPU. I personally feel monitor never give 100% accurate readings. It only shows approximate results.

Normally this happens if you are doing things like - copying over 2 GB size files, Running apache, sql, xsp, etc servers side by side, editing or rendering videos, writing DVD disks etc.

Playing any graphics game means video editing on the way. You are continuously editing the images. Thats why it shows such high cpu usage. Its normal. Any graphics related application takes huge ram and lots of processor cycles to run.

May be different OSs calculates and shows CPU usage differently. May be mac shows processor usage by processes not as a whole. I only used windows and Ubuntu.

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Perhaps it could be because you are using more than just what your CPU normally handles (not very useful, I know, but meh)

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