A PC bottleneck occurs when one component in your computer holds back the performance of another. In gaming, this usually involves your CPU (Processor) and GPU (Graphics Card). If your GPU can render 200 frames per second, but your CPU can only process physics and game logic for 100 frames per second, your CPU is bottlenecking your system, and you will only see 100 FPS.
CPU vs GPU Bottleneck
CPU Bottleneck: Your graphics card is waiting for your processor to catch up. This often happens at lower resolutions like 1080p, or in CPU-heavy games like esports titles (CS2, Valorant) and simulation games. Upgrading your CPU or increasing graphical settings/resolution can help.
GPU Bottleneck: Your processor is waiting for your graphics card to finish drawing the frame. In gaming, a slight GPU bottleneck is actually considered ideal, because it means you are getting the absolute maximum performance out of your most expensive component (the graphics card).
Does Resolution Matter?
Yes, significantly. As you increase your resolution from 1080p to 1440p to 4K, the workload on your GPU increases exponentially, while the workload on your CPU stays mostly the same. A CPU that severely bottlenecks an RTX 4090 at 1080p might be perfectly fine for that same graphics card at 4K.