AMD HD7970 vs. NVidia GTX680: FPS vs. Frame Latency

Until a year or so ago, all the graphics card reviewers were going by the conclusion: more FPS ⇒ smoother gameplay. Sure, there isn’t anything wrong with that conclusion, if you keep rest of the parameters the same. But that actually is not the case.

People who have bought AMD’s HD7900 series high-end cards have been really pissed to find out that their gameplay is not actually as smooth as those reviewers suggest. 60FPS means pretty smooth gameplay. You might not see any difference between 60FPS and anything higher. Funny thing is that, people are actually getting the FPS that the reviewers claim – there is no mistake there. But for some reason, gameplay isn’t smooth. You would see pauses every few seconds. If you run a frame rate counter, such as FRAPS or MSI Afterburner, you would not notice any glitches. But you are NOT feeling that the gameplay corresponds to which the FPS counter is showing.

Guess what? That’s because of “micro-stuttering”. The phenomenon called micro-stuttering happens when a certain frame takes abnormally longer to render than the previous subsequent frames did, and his being repeated over and over the entire time. (That last part is important to create the illusion of stutter.) If you plot the frame times in a graph, you would see spikes appearing roughly in similar gaps. Funny thing is, if you average out the FPS, you would not see a drop. That’s why you cannot go with just the FPS.

Look at the following example.

Say, you are getting 50fps in your game. It could either be that all of your frames took 20ms each to render (1000ms per second/20ms per frame = 50fps), or it could be that the first 49frames took 19 seconds each (931ms total), and the last one took 69ms to render. 50 frames, 1000ms ⇒ 50fps It would still give the 50FPS, but you would be seeing terrible micro-stuttering in the latter case.

Pros and Cons of a Single-GPU system over a Multi-GPU system

Most people are in the opinion that you can get two low-end or midrange GPUs, set them up in SLI or Crossfire depending on the GPU maker, and get similar or more performance than a high-end single GPU. They would usually get that idea from the reviews. But most reviews would only talk about the FPS that is reported to them and conclude that the multi GPU setup gives more to the consumer, but they forget to mention a lot of things in the process.

But in reality, you should not build a multi-GPU setup if it is utmost necessary. Let’s first see why you should not build a multi-GPU setup.

Pros of Single-GPU setup over Multi-GPU setup

1. Smoother gameplay even at a lower reported FPS value

That is insane, right? How can lower FPS be smoother than higher FPS? That is because the phenomenon called micro-stuttering. You would get very annoying, small pauses that are noticeable to eye, but not to the FPS monitoring apps such as FRAPS which record the frame count in a second. The frames are spread equally inside that second. Say 30fps. You might get 20 frames in the first half second and 10 frames in the second half second. This difference is noticeable to the eye and it is very difficult to the eye. Basically, how much noticeable it is, depends on the person, the game and even the other components of the PC. There is no clear cut answer to this problem from either GPU maker.