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CPU Usage %

Markleshark

Markleshark

macrumors 603
Original poster
So, basically, its just one of those things I don't know...

I was wondering if someone (Pretty broad question, I know) could explain how CPU usage percentage works. Coz I have a CoreDuo Mac Mini, all that I understand, one processor, 2 cores, etc, etc. So will that show as 200% CPU, or is that for 2 physical processors?

Just an explanation would be nice, just one of those things I've not really got round to understanding.

Cheers Peeps
Mark
 
um, I was under the impression that it was only 100% total (admittedly more windows based on this)

each cpu/core is equal to 50% of the overall performance of the system/cpu. The individual graphs show the percentage of that 50% that is being used on each core/cpu.

So say you have 1 core running at 25% and the other at 50% use the overall use would be (25% of 50% = )12.5% and (50% of 50% =) 25% which would give a 37.5% overall cpu percentage.

If both cores/cpus are running at full speed (ie 100% each) then the overall cpu percentage would only be 100% due to the fact that 100% performance for the cpu/cores would be the combined performance of the cpu/cores.


Maybe macs register the information differently to pcs but the above is my understanding of it.
 
I don't know how it works in Windows, but in Activity Monitor 100% does represent only a single CPU core, as robbie said.
 
LeviG said:
Maybe macs register the information differently to pcs but the above is my understanding of it.
Click to expand...

OSX is a Unix so follows the long established Unix standard process of each core or CPU being 100%. So on a Mac Pro you can have 400%!
 
Thanks for the replies guys, as I say, just something I never got my head around.

However, when I take a picture of AM, I still get 2 graphs, for both cores, but the usage percentages only add up to 100%. Will I see more percentage as I do more CPU intensive things (Video Encoding, etc)
 

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Nutter said:
I don't know how it works in Windows, but in Activity Monitor 100% does represent only a single CPU core, as robbie said.
Click to expand...

windows has two ways of displaying the graphs
1) single graph showing current cpu usage total (100%) with a single window showing history/current cpu usage.

2) single graph showing total cpu usage (100%) and 2 or more graphs showing cpu history/current cpu usage

the history/current cpu has no numbers saying actual amount though.

EDIT: although this is only in task manager other programs available display the same info slightly differently
 
Here's Maya rendering with mental ray on a quad. The bottom bar is a utility that shows total use of each cpu.
 

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Markleshark said:
Thanks for the replies guys, as I say, just something I never got my head around.

However, when I take a picture of AM, I still get 2 graphs, for both cores, but the usage percentages only add up to 100%. Will I see more percentage as I do more CPU intensive things (Video Encoding, etc)
Click to expand...
Keep in mind that you've only got it set to show your processes, so those of the system and any other logged-in users won't show. Set it to "All Processes" (top rightdrop-down) to see them all.
 
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