How does video processing actually work?

[ShawnD1]

Recently I have seen people say that having a slow processor actually limits the ability of a video card. Is this true?
If the above is true, is there any point where a faster CPU does not make higher fps?
When using something like OpenGL, does the CPU just send stuff to the video card to process or does the CPU do some rendering on its own like software rendering?

 

[BFG10K]

Recently I have seen people say that having a slow processor actually limits the ability of a video card. Is this true?

Yes.

If the above is true, is there any point where a faster CPU does not make higher fps?

Yes but it depends on the game, the GPU, the CPU and the settings you're running the game at. Every situation is different.

When using something like OpenGL, does the CPU just send stuff to the video card to process or does the CPU do some rendering on its own like software rendering?

The CPU does not do "software rendering" per-se but it does all of the functions that GPUs can't do. Modern GPU pipelines start with raw vertices so everything else that is required to get these vertices (eg the game engine, networking, sound, AI, scene preprocessing etc) is handled by the CPU. When the CPU is finished the vertices are transferred to the GPU across AGP and the GPU begins working on them.

This initial stage is completely CPU limited and having a slow CPU here will bottleneck the GPU because it'll be twiddling its thumbs, waiting for the data for the next frame to arrive. Likewise, if the GPU is still working on the last frame when the next batch of vertices arrive then the GPU becomes the bottleneck as the CPU is able to feed data faster than the GPU can process it.

 

[AgaBoogaBoo]

BFG10K is correct, but it may be simpler to understand that the GPU and CPU handles things differently. You can't try making a ferrari engine work with a harley, and the other way around too. In many cases in today's newer games, unless you have a CPU thats pretty old, it won't matter. In games, you'll benefit more from a better GPU, but again, it depends on the type of game. There are some games that are CPU bound, others are GPU bound. BUT, lets say the game is GPU bound, then no, the cpu won't really matter. There are some games where using a Radeon 7200 and a 9800 may show little or no difference. There are other situations though, where the GPU is a bottleneck, and using a P4 2.4C Ghz or a 3.2Ghz can make little/no difference.

It all depends what you want to do.