Where graphics performance was once determined solely by processing power, it’s recently become a matter of numbers. With technologies like Nvidia’s SLI and ATI’s Crossfire, it’s not a matter of necessarily how big your video card is, but how many you have that counts. There’s no doubt about it that SLI has been a huge success. Benchmarks are now higher than ever.
However, there’s a caveat to consider. What isn’t advertised on the front of that 9800 GTX box is that two or more video cards running in SLI don’t officially support dual monitors – At least not from the manufacturer. I found this out when building my latest PC and I was crushed. I’ve used dual screens for 4 years now and I couldn’t imagine life without it. The “official” solution is to disable SLI when using dual monitors. Who has that kind of time?
A simple search on the SLI Zone forums shows a number of people who share the same frustration. Thanks to member FredrikMH, Dual monitors while in SLI are possible through a simple list of steps – And a few requirements.
To accomplish this, you’ll need:
- 2 Nvidia SLI-supported graphics cards (for a list of cards that support sli, click here)
- 1 PCI (Not express) graphics card. I used an 8600GT. A quick note, while you shouldn’t spend $250 on a card that solely supports a second monitor, if you ever plan on running visualizers or playing video on this screen, you’ll need a halfway-decent card. Don’t go shopping in the bargain bin at tiger direct (this also means you’ll need a spare PCI slot on your motherboard – This might work on a 3 slot PCI-E motherboard, where only two cards are running in SLI).
- Vista (some people report problems doing this in XP – try at your own risk)
I’ll remind you again, this isn’t officially sanctioned by Nvidia. So try this at your own risk (I don’t take responsibility if you fry your brand new video card – or any part of your computer for that matter).
Note: While I refer to the “third” card (PCI) throughout this article, this should work with any SLI configuration, including tri or quad setups.
How does it work? The SLI-enabled cards power the main screen (as intended). The third card powers the secondary monitor. The problem is that when you enable dual monitors on cards running in SLI, the SLI is disabled. SLI works (essentially) by dividing the processing requirements of the main display among the graphics cards. For example, if you have two SLI cards, each only has to work on half of the main screen. This means one card can display half of the content much faster than if it had to power the entire display on its own. If dual monitors were allowed on cards running SLI, the concept would bust as each card would be taxed by 1 monitor. The trick is to bring a third card into the equation after the fact. By letting the third card power the second monitor, the SLI-enabled cards can wok on the main display (the one running the games).
The steps:
- Start by installing all cards into the computer (including drivers). Drivers can be downloaded here. Connect your main display to the first header of your top SLI card (typically will be the top-left most DVI port on the back of your machine. Connect your second (and third, if you want) monitors to your PCI card.
- Disable the third (PCI) card in device manager. Right click on ‘My Computer’ (or ‘Computer’ in Vista) and click ‘Manage’. Select ‘device manager’ and expand display adapters. Right click on the PCI card and choose ‘Disable’. Select yes if a confirmation box appears.
- Restart your machine
- After the machine restarts, go into your Nvidia control panel (Start Menu->Programs->Nvidia Corporation->Nvidia Control Panel->Control Panel) and enable SLI.
- Restart your machine
- Some people report that at this point their PCI card that they disabled in step 2 was automatically enabled. Mine wasn’t. If yours isn’t, do so now by following the steps from #2 (and selecting enable).
- Right click on your desktop and select ‘Personalize’. Choose ‘display settings’ from the window that appears. You’ll see a visual representation of your screen capacity. Select the display labled ‘2′ and check the box ‘Extend the desktop onto this monitor’ below (follow the same steps for a third monitor – display ‘3′). Hit OK at the bottom of the window. Your screens will flicker and you’ll be good to go. Make sure to select ‘OK’ in the confirmation box that appears or else your settings will revert.
After doing this, you’ll be unable to make any changes to your SLI configuration without first disabling the PCI video card in device manager. In addition, you won’t be able to really “know” if SLI is in fact enabled – As far as Vista is concerned, it isn’t. However, have faith, as it really is working. If you “have to know”, download GPU-Z to find out (it will say enabled or disabled at the bottom of the window).
For the original post at SLI Zone (with pictures and helpful posts), click here.
That’s all! Thanks, and happy computing!