NVIDIA SLI & the Flickers

I just wanted to keep all of you curious folks up to date on my latest computer update. Because I know you are all furiously curious.

The computer I built 2 years ago is still keeping up with the latest software so I've seen no reason to build a new computer.

However, as the graphics in games get more demanding I decided to do an experiment. I decided to install a second video card to take advantage of NVIDIA's SLI technology. Basically leveraging the GPU's of two graphics cards to give a performance boost.

My first mistake was assuming the graphics card would come with the little SLI link cable.

I opened the case, installed the new video card in the second slot and turned the computer back on. Voila, the NVIDIA driver detected that there was another video card and set it up as SLI. I was shocked at how easy it was. But then I got an error message about "video link not detected".

My first reaction was to re-check my video card box for a missing cable, but it was empty. My second thought was simply a sinking feeling. Then, I did some research.

It seems the link cable in question is normally shipped with the motherboard. I have an ASUS P5N motherboard and I still had my box so I looked in it and sure enough, there was a cable just like the one pictured above. It's obvious where to connect it on the NVIDIA graphics cards. If you need a diagram, you probably should put the cover back on your computer and carefully back away from the machine.

Then, I ran my first game and I got these bluish artifacts and flickering while running. And I got another sinking feeling. My power supply only had one power plug for supplying power for video. Obviously with a second card I needed another plug. The new video card came with a power plug adapter. You basically had to plug two standard plugs into this one adapter to create one video card plug. All the web sites I visited said that the flickering was more than likely a power problem.

My mistake: I used a standard plug that was daisy chained to a case fan. I took another look in the case, did some power rearranging and produced two dedicated standard plugs to feed the video plug adapter. You might have to read that twice.

I turned everything back on and it's been running flawlessly ever since. It seems smoother, but unfortunately I didn't do any performance tests for a before/after comparison. I don't know that it would have made a difference. When you have two of something it's not always faster, but often times smoother. I don't know that I've seen a performance test that measures smooth.

You see performance tests all the time that say, "I get 60 frames per second", but you don't often see a run over time with various activities where you maintain an average of 40 frames per second with a low of 10 and a high of 60. I suspect that having two GPU's would mostly produce a more stable frame rate with a better average and a higher low, but I don't feel like proving it.

Another thing to do if you intend to try SLI is to go in the NVIDIA control panel and make sure it says SLI is enabled. After experimenting with mine, it somehow got switched to disabled and I had to re-enable it. There was no warning except just to check it and see that it was disabled.