CPU usage explanation?

[whitedragon101]

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?

 

[GGJstudios]

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.

 

[whitedragon101]

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.

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%?

 

[GGJstudios]

Any 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%?

Yes.

 

[whitedragon101]

Yes.

Thanks