CPU Bottlenecking - Why?

[Caviman2201]

Can anyone give a clear thorough explanation of what exactly CPU bottlenecking is (I know that its a decrease in framerate given the same video card but a weaker processor) and why it ceases to matter at higher resolutions?

It seems like every review I see will show that at resolutions like 1920x1200, you can use anything from an Athlon X2 to a C2Q and the fps will not change more than a couple frames, but drop the resolution down to 1280x1024 and all of the sudden, you're talking about a HUGE difference in FPS. I'm just curious as to why as the resolutions go up, the burden of rendering shifts from CPU to GPU...

[Evilsizer]

Can anyone give a clear thorough explanation of what exactly CPU bottlenecking is (I know that its a decrease in framerate given the same video card but a weaker processor) and why it ceases to matter at higher resolutions?

It seems like every review I see will show that at resolutions like 1920x1200, you can use anything from an Athlon X2 to a C2Q and the fps will not change more than a couple frames, but drop the resolution down to 1280x1024 and all of the sudden, you're talking about a HUGE difference in FPS. I'm just curious as to why as the resolutions go up, the burden of rendering shifts from CPU to GPU...

because when its at higher res's with aa/af the gpu is the bottleneck. as the cpu only needs to be able to feed so much data to the gpu at X res vs Y res. at lower res's with no aa/af the more data you can feed the gpu because its not working as hard at a lower res, its able to render frames faster. as at higher resolutions your talking bigger texture sizes which is why video cards now come with more memory to handle higher resolutions. then when you use aa/af it then makes the gpu go back thru those same high res texures to reduce/remove jaggies and increase texture quality. with those not being used the gpu doesnt have much work to do...

[vlaszlo]

Imagine a 1 pixel video card.
This card will render all 1 pixels in 1 pico-nano seconds,
the cpu must work hard to keep the gpu busy.

Then imagine a second card with 1 billion pixel.
The card wil render the frame in 1 year,
so the cpu can go to drink beer, and return after 1 year idling.

Think about it.

[Caviman2201]

ok... I'm getting it... thanks for the explanations, guys.

So one could say that its also true that if you like to play with a lot of AA/AF (as opposed to high resolutions), CPU doesn't matter as much... If you typically run at 1280x1024 and you are playing a game that isn't stressing the card much (say, BF2), you can pretty much turn on AA/AF to the max for free because turning those on isn't making the CPU work any harder... just the GPU.

[Evilsizer]

video card do take hits in FPS when using AA/AF. though certian cards like the new Ati 4000's dont take as big a hit with aa/af vs the NV 8000/9000/GTX200's.

[vlaszlo]

My friend has some celeron and 9600GT, he plays every game with 16x AA.
But cant play games in wich are better physics.

I woud better call this cpu bottleneck, CPU Limited and GPU Limited instead.