Why CPU limitations at low res?

[NickelPlate]

Hi All,

I've read this many times here but don't understand why people say that games are CPU limited at low resolution but not at high resolutions. Why would a game be less CPU bound at higher resolution? Intuitively, it seems like running at a lower resolution would always give better performance regardless of hardware.

However, my own experience seems to indicate that indeed performance is better at higher resolutions with certain hardware. Particularly this is true since I just upgraded from a 6800GT to an 8800gtx.

Initially, gaming performance was nearly the same as my old card but at higher resolutions things got much better. More CPU overclocking really seems to be unlocking the potential of my 8800gtx. But again, at lower resolutions (1280x1024 and lower) the new card doesn't really perform any better. Why? Am I getting better performance at higher res because the refresh rates are lower? (I run vsync on). Of course I'm running a single core CPU and I think now that's my biggest limitation. I guess a C2D upgrade is in order to really enjoy the benefits of this card.

Any thoughts?

NP

Current System Specs:
Intel P4 630 HT 3.0 @ 3.6Ghz (Prescott)
EVGA 8800gtx
Asus P5GD2 Premium Mobo
2 gigs Crucial Ballistix DDR2 667 (PC2 5300)
Raptor 150 HD
Soundblaster Xfi Music
Sony 19" Trinitron
OCZ Gamexstream 850 PSU

 

[mozirry]

You are thinking of it in a wierd way.

Your frame-rate may be more CPU bound at low rez due to the fact that at a low rez your video card really isn't doing much.

So you will have a 100+ framerate at 640x480, 100+ framerate at 800x 600, then as you get higher in resolutions the games framerate will begin to drop due to the power needed from your video card.

I still wouldn't say though that a game is "CPU limited at low resolution but not at high resolution". I would say "Video cards are more important at high resolutions then the CPU"

 

[Rangoric]

Originally posted by: mozirry
You are thinking of it in a wierd way.

Your frame-rate may be more CPU bound at low rez due to the fact that at a low rez your video card really isn't doing much.

So you will have a 100+ framerate at 640x480, 100+ framerate at 800x 600, then as you get higher in resolutions the games framerate will begin to drop due to the power needed from your video card.

I still wouldn't say though that a game is "CPU limited at low resolution but not at high resolution". I would say "Video cards are more important at high resolutions then the CPU"

I agree.

Think of it this way.

Your CPU can run the game at one framerate, this framerate does not depend on the resolution. So if its 1680 x 1050 or 640 x 480 the game will run at the same rate.

Your GPU can run the game at one framerate, dependant on the Resolution. If its 1680x1050 it will run slower then at 640x480.

With this in mind lets say your GPU is capable of 100fps at 640x480 on up to 1280x1024 but only able to do 40fps at 1680x1050. Now lets say your CPU is capable of 80FPS no matter the resolution.

At the lower resolutions like 640x480 your CPU will only let you run at 80FPS, so your bottleneck is the CPU. When you get to 1280x1024 its the same issue. However at 1680x1050, your GPU is only capable of 40FPS while your CPU can push 80fps you are bottlenecked by the GPU doing only 40fps. A video card that does better at that 1680x1050 resolution can bring you back UP TO the CPU speed of 80FPS.

 

[NickelPlate]

Makes sense now. Thanks guys.

NP

 

[NickelPlate]

Makes sense now. Thanks guys. Oops double post, sorry.

NP