Ever since nVidia came up with their SLI (Scalable Link Interface) PCI express video cards a long while back I've been eyeing them greedily, but I'm leary of spending my hard earned pesos on new technology that might or might not work properly.

For those of you not familiar with the technology, we first saw SLI in the old 3dFX Voodoo 2 video cards. (Never owned a Voodoo? Damned kids. :P) The theory is that you can chain multiple video cards together each rendering a different part of the screen to boost performance. With the old SLI (Which meant Scan Line Interleave btw, just in case that ever comes up in a Trivial Pursuit game) each card would render one line on the screen, so card one would do the first line, card two would do the second, card one would do the third and so on. With the new nVidia SLI, card one renders the top half of the screen and card two renders the bottom half. In theory you've got two GPUs (Graphics Processing Unit) working together so you should see a significant performance increase, in theory of course.

A few weeks ago I finally caved and upgraded our test system to PCI Express and SLi. It was much, much easier than I thought it would be. I was prepared for an epic battle against good and evil to get this thing working and instead it was literally plug n' play. I had most of the items I needed to get this thing up and running, all I needed was a new mobo and video cards. The motherboard selected was the MSI K8N SLI due to the fact that I really like MSI's equipment. I sell a large amount of it at work and very seldom have any problems with it and it performs well. The other reason it was picked as for ease of SLI setup. I've seen quite a few motherboards that have banks of jumpers or something equally stupid that must be all changed to set the board or SLI or non-SLI. This normally wouldn't be a big thing as once you have it setup for SLI it's pretty unlikely you'd be running it with a single video card unless one failed.. But still, I like simple. The only board I've seen simpler than the MSI is some of the ASUS boards, where you simply make a change in the BIOS to enable or disable your SLI. The MSI solution is a small board, rather like one of the old COAST cache modules, that sits in a socket on the motherboard. Pop it out, flip it over and SLI is on. The SLI board is clearly marked.

One little board flipped over enables zee SLI goodness!

The video cards chosen were the MSI NX7800 (Geforce 7800GT) for their alleged performance and price, along with the fact that again I just like MSI. I was interested in going one step up but when we're talking about two video cards it's a little on the expensive side. That is the one download to SLI... It's not just a one card upgrade, you have to do both. I've been interested in the ATI Crossfire solution but since it's never shown up and the fact that I want pixel shader 3 support, hell with them, it's back to nVidia we go!

Yes. Oh yes. Yellow slots of joy.

Installation was a snap. The video cards lock into thier respective PCI-E slots and the little jumper card that came with the motherboard joins them together. One little pieced of advices I have is to put a little hot glue on this connector board, as it will start to come loose if you move your system around quite a bit. I take my machine to work with me every day, and after about a week I noticed the card has almost worked it's way right off.

Once everything was installed into the system we powered up and loaded all the drivers. The previous motherboard was an nForce 3, so Windows XP didn't seem to have any problem detecting all the nForce 4 goodness on the new board. I was prepared to do a Windows repair install on this one but thankfully it wasn't required. Once all the drivers were loaded and the machine restarted we had a popup near the clock that announced "SLI capable system. Click here to enable." Click on the window, then put a checkmark on the "Enable SLI multi-GPU" box and restart the computer and it was done. That's it. Can't think of many ways it could be easier.

Enable multi-GPU? Why yes. Yes please.

One interesting thing that really messed me up was the "Show GPU load balancing." I turned it on then couldn't figure out what the hell this line I had in World of Warcraft was. (I'd forgotten I'd enabled it) Thanks to Belial for helping me figure it out. The load balancing puts a line down the middle of the screen to show you which portions are being rendered by which video card, and what the load is like on each with two green bars.

Come on GPU2 you slacker! RENDER THAT LOWER SCREEN!

The first benchmark I ran on the new cards was the most excellent Aquamark. I was rather suprised when my Aquamarks were only slightly higher than they were with the ATI X800Pro that the 7800s had replaced. The only test that was significantly higher was the Massive Overdraw test, which was much quicker on the SLI cards. We moved on into the other tests we use, and that's where we truly saw some big differences. Sadly I didn't get any Doom3 benchmarks on the X800. Please note that settings for the video card were left at default, and the Forceware 78.01 drivers were used. The processor in the system is an AMD Athlon64 3500+ at stock settings. Memory is 4x Corsair 512 DDR PC3200 XMS Pro again at stock settings.

Here's the final results for all the tests: