Bottlenecking is discussed as a yes-or-no property of a pair of components. It is neither yes-or-no nor a property of the pair, and the framing causes people to buy the wrong things.
In short
- Every system is limited by something. That is normal, not a fault.
- Which component limits you changes with resolution, settings and workload.
- Measure it on your own machine rather than reasoning about it.
- A processor limit at 1080p may disappear entirely at 1440p.
What is actually happening
Producing a frame requires work from both the processor and the graphics card. The processor handles game logic, physics, and preparing draw instructions. The graphics card renders.
They work in sequence, so whichever finishes its part last sets the frame rate. If the processor takes 10 ms and the card 6 ms, you get roughly 100 frames per second and the card waits. That is a processor limit.
There is always a limit. A system where neither component is ever the constraint is a system that is not doing anything.
Why resolution changes the answer
The processor does approximately the same work per frame regardless of resolution. It prepares the scene, and the number of pixels is not its concern.
The graphics card does dramatically more work at higher resolutions, because it renders every pixel.
So at 1080p the processor is more likely to be the limit, and at 4K the same pair will almost certainly be limited by the card. The same two components, differently balanced, purely because of the display.
How to find out
Run what you care about while watching processor and graphics card utilisation.
Graphics card at or near 100 percent means it is working as hard as it can and is the limit. That is the desired state while gaming.
Graphics card well below 100 percent with one or two processor threads pinned means the processor is the limit, and a faster card would change little.
Five minutes of this tells you more than any amount of reading, because it looks at your machine and your games.
Why total CPU usage misleads you
A common mistake is looking at overall processor utilisation, seeing 40 percent, and concluding the processor is not the limit.
That figure is an average across all cores. A game that depends heavily on one thread can have that thread completely saturated while the others idle, and on a sixteen-thread processor one saturated thread shows as roughly 6 percent of the total.
Look at per-core usage instead. One or two cores pinned near 100 percent while the overall figure looks comfortable is the signature of a processor limit, and it is invisible if you only watch the summary.
What a processor limit feels like
The experience differs from a graphics card limit in a way worth recognising, because it points at the cause without any monitoring.
A graphics card limit generally produces a lower but steady frame rate. Reducing graphics settings raises it.
A processor limit produces a frame rate that is fine most of the time and drops sharply in specific situations: a busy area, many characters on screen, a large base in a strategy game. Lowering graphics settings changes nothing, because the graphics card was never the constraint. That last detail is the clearest test available and costs nothing to try.
What to do about it
Check the memory profile is enabled first. Memory running below its rating hurts processor-limited performance noticeably, and a surprising number of machines are running slower memory than they contain.
Check background software. A processor-limited game competes with anything else running, and browser tabs with video, overlay software and launchers all take a share.
Raise the resolution, which sounds backwards but works. Moving from 1080p to 1440p shifts work onto the graphics card and away from the processor, so you get a better looking image at a similar frame rate, using capacity you already own.
Replacing the processor is the last resort rather than the first, particularly on an older platform where it means a board and memory too.
Being processor limited is not automatically a problem. If you are getting a frame rate above your display refresh rate, the limit costs you nothing. It only matters when the frame rate you get is below the one you want.