ATI Radeon HD 4000 Series discussion

[Sr7]

Ignorant people will buy 4870x2 because they have no idea about the stuttering issues of CF; and will drool at the FPS numbers whereas their gaming experience is no way near that FPS.

That's of course, unless ATI has magically solved the problem, made all frames nicely sync'ed and with no loss of FPS in comparison to regular AFR.

That's part right part wrong.

3d graphics do what is called a present call to display the image that has been rendered in the back buffer. If you have multi-gpu, often they don't present at regular intervals because you're not talking about 1 pipeline, you're talking about 2 pipelines trying to feign 1. So if they go:

10ms
Present
3ms
Present
10ms
Present
3ms
Present

Instead of the single GPU approach:

10ms
Present
10ms
Present
10ms
Present
10ms
Present

You *DO* get double the frames rendered and you're legitimately getting that higher framerate, but it doesn't *feel* that way because the presents are imperceivably close together. So while you do get double the framerate, sometimes (more often when framerates are low) you don't get the actual perception benefit (smoothness) of that higher framerate... it still chews through the frames but doesn't present them nicely for your eyes, so the benefit of getting more FPS is pretty much lost.

Keep in mind most of the time the few millisecond variation is no big deal (un-noticeable) but at lower framerates it can be.