Eli5: How is it that my CPU is operating at a 3 GHz speed but utilization is 50%, and sometimes the speed is 1.8 GHz but utilization is 100%?

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I mean, what’s the difference between both? Why do I never see 100% utilization at 3 GHz even when using the most resource intense tasks?

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4 Answers

Anonymous 0 Comments

the cpu utilisation percentage is based on CPU time, essentially the operating system assigns each program a set amount of time slots to use the CPU, after the time is up the operating system takes back control and decides what program to give control to next and for how long

CPU utilisation is essentially how much percentage of the time slots the operating system has available is being used by programs

The cpu speed is not necessarily linked to this, for example laptops might lower clock speed even on high load to save on battery life

Anonymous 0 Comments

Your CPU has multiple threads. When it does one task with one thread it can go pretty fast, but doing something complex with all of its threads it uses more energy and it heats up, and the top speed goes down.

This is why on benchmarking websites you’ll see single and multithreaded speed scores. My CPU tops out at 4.8ghz single threaded but goes down to 4.5 when its stress testing all threads.

Anonymous 0 Comments

Your CPU has multiple cores. If you are doing a resource intensive task that doesn’t take advantage of the multiple cores then you’ll have some cores at 100% and some cores scratching balls so the overall CPU usage is less than 100%

Anonymous 0 Comments

There can be many reasons why your CPU is almost never at its highest clockspeed when fully utilized

It might be power constrained, meaning that when running all of its cores, it cannot draw enough power to keep going faster

It might be thermally throttling, meaning that it runs too hot to draw more power and run faster

There can also be architectural constraints why these things happen, like signal integrity, which can be correlated to power draw and thermals. Suffice it to say, that every CPU on the market has higher clockspeeds when using just one core compared to using all of them at capacity