Monday, September 3, 2012

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.

2. Crossfire can be a hit or a miss. It’s always a hit with a single GPU.

Some games do not support multi-GPU at all. So in the worst case, you will be running the game even slower than what one of your lower-end cards can run it. This is because there can not only be zero scaling, but there can be negative scaling too! Also there can be all sorts of driver problems depending on the cards, the driver version and the game.

3. Lower power draw.

Which means, you don’t have to get a massive power supply to begin with. Smaller PSU means cheaper. Lower power means your electricity bills are not that high. I am seeing a noticeably lowered electricity bill, going from HD6950 Crossfire to a single GTX670.

4. Less heat and possibly lower fan noise

Lower power consumption comes with lower heat dissipation. Lesser the heat, slower the fans have to spin. Now you have one cooler instead of two, but it may or may not mean lower fan noise. You might have to spin the fans on the high-end GPU faster than the fans on the lower-end GPUs because of the TDP difference.

5. No need to specifically get a SLI or Crossfire ready motherboard

Most motherboards come with SLI and/or Crossfire support these days, but not all of them come with full bandwidth PCI-E slots. Lower-end motherboards may either come with a single PCI-E slot or a x16 + xx slots. Unless you have can at least do dual x8, you should not use multiGPU – because the lack of PCI-E bandwidth might noticeably narrow the performance gap between the single high-end GPU and the lower/midrange multi GPUs.

6. Video RAM doesn’t double with SLI or CF

If you are thinking that your midrange 1GB dual card setup is a match for 2GB high-end single  card setup, you cannot be any more wrong. Video RAM doesn’t double with either multi GPU technology. You can only use the amount on a single card because the data is copied between them, not shared. (Just like multi processor setups compared to multi-core setups). It gets worse if the cards have mismatching amount of RAM. You will only be able to utilize the amount of RAM in the lower-end card.

Pros of dual/multiple-GPU setup over Single-GPU setup

1. High-resolution gaming

Just imagine, 1600p requires twice the power of a 1080p gaming pixel fill wise. It doesn’t get any better with 3-displays (or more) or 3D or both. But the problem is, you cannot settle for two low-end/midrange cards for high resolutions. You have to go with multiple high-end cards. Talk about exponential expenditures.

2. Bragging rights!

Heck, you can boast around. While boasting is bad, but you at least get some self-satisfaction. Tom Logan is using two GPUs in his Orca project only for the looks! Talk about 1st world problems.

3. It’s good on the benchmarks

Benchmarks that don’t really care whether it is smooth or not. You only look at the FPS count in benchmarks. Actual gameplay is better on a single GPU setup. Benchmarking actually will sound like a stupid thing, but there are professional benchers and world record breakers. I think they get paid something: monetarily or morally. :D

Conclusion

So that’s it. I would only consider dual GPU setup over the single GPU setup if I have a high resolution display. In every other scenario, you are wasting money and getting your blood boiled.

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