this post was submitted on 27 Jan 2025
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I'm self studying for a server+ cert and ran into this paragraph. Am I right that CPU time is a set of ticks utilized, the CPU Capacity is the total capacity, and the CPU usage is the percentage of ticks:capacity?

I have been making notes from this chapter, and the more I get into it the more I seem to find things like this that seem slightly off.

Does anyone have a physical copy of the 2ed McMillan CompTia Server+ study guide I can compare against? I feel like someone is messing with me.

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[–] [email protected] 2 points 3 days ago (1 children)

You are correct. Here’s a thread on how CPU usage is calculated:

https://stackoverflow.com/questions/3748136/how-is-cpu-usage-calculated

It’s basically (CPU time of the process) / (clock time), or (CPU time)/(clock time * number of hardware threads), depending on how it’s reported.

Note that there’s are some complications here, like the time “wasted” context switching or running the OS.

[–] [email protected] 1 points 3 days ago

Thanks, good thread. I'm not sure if that's one I referenced to confirm what I suspected, but it is very clear.

[–] lurklurk 1 points 3 days ago

Sounds about right...

Cpu time is the time your process actually uses the cpu to process things, rather than waiting.

It's often shown as a percentage in top and other performance monitors. So 10% means it's spending 1/10th of the time actually calculating things

[–] [email protected] 1 points 3 days ago (1 children)

Try elaborating on what "CPU Capacity is the total capacity" means and I think that'll get you the rest of the way to understanding this topic.

[–] [email protected] 2 points 3 days ago

Above it says that CPU usage is the total capacity of the CPU to perform work. When I say CPU capacity is the total capacity, I mean in ticks or seconds, depending on the measurement.

What I'm struggling with is that the text says that the CPU time is a subset of the usage expressed as a percentage. It seems to me that it is incorrectly identifying CPU usage as CPU capacity.