CPU usage explanation?

Discussion in 'OS X Mountain Lion (10.8)' started by whitedragon101, Oct 8, 2012.

  1. macrumors 6502a

    Joined:
    Sep 11, 2008
    #1
    OSX ML activity monitor. I don't quite understand it:

    There are two parts the CPU % usage per process in the big table and the 3 figures at the bottom, user, system and idle.

    Question 1)
    The figures at the bottom. If the CPU is 80% idle on a quad core machine, this usually means the fans are blasting at full speed ( and volume). Does 0% idle mean 4 cores at 100% and therefore that 75% idle means an effective load of 1 core at 100%?

    Question 2)
    i thought maybe main table displaying CPU % per process shows the % of the current CPU load being used by a single process? I.e if the CPU is 80% idle and a process is 100% that would mean it is using 20% of total CPU load. But that can't be right as the percentages often add up to more than 100%. How does the CPU % per process work?

    Question 3)
    How come even multicore video encoding doesn't get the CPU past 50% idle yet spins up the fans and temps to the max?
     
  2. macrumors Westmere

    GGJstudios

    Joined:
    May 16, 2008
    #2
    Yes, it's 100% per core. A quad-core computer is capable of up to 400% CPU utilization. A dual-core, 200%. Your temps are primarily driven by high CPU and GPU activity, but there's not necessarily a direct correlation between percent of CPU utilization and temps.
     
  3. whitedragon101, Oct 8, 2012
    Last edited: Oct 9, 2012

    thread starter macrumors 6502a

    Joined:
    Sep 11, 2008
    #3
    And the main user, system, idle figures at the bottom? Is 0% idle all 4 cores at max and 75% idle the equivalent load of 1 core at 100%?
     
  4. macrumors Westmere

    GGJstudios

    Joined:
    May 16, 2008
    #4
    Yes.
     
  5. thread starter macrumors 6502a

    Joined:
    Sep 11, 2008
    #5
    Thanks :)
     

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