Imagine a task as a rectangular peg, where the width represents the number of threads and the height represents how intense it is.
Imagine the CPU as a hole where the width is the number of cores, and the height is the single-threaded performance.
You can imagine easily now how you might never fill the hole (reach 100% usage), but still be unable to fit the peg through the hole.
Edit: To expand more on why your CPU chart would appear the way it does (ie, misleading), the answer is it has to do with the windows scheduler. If you have an i5 and every chart is hovering around 50%, that doesn't actually mean you have 4 threads that are each using ~50% of a core (well, it could mean that but it's extremely unlikely). It means (most likely) you've got 2 intense threads that are each maxing out a core - or at least, the equivalent of 1 core - and Windows is moving that load around constantly so while it looks like each is 50% loaded, in reality, 2 cores are pinned and two are idle, and they just trade off which is which very often.
keripton10 reacted to vanished in Can a CPU be a bottleneck without hitting 100% on ANY of the cores?
