Tom's Hardware > Forum > Graphic & Displays > Graphics Cards > 3 monitors, 2 cards, no sli
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judgedee   08-27-2008 at 12:19:19 AM

I am looking for help setting up a 3 monitor display for gaming. The gaming display is to stretch from the center of the left monitor, across the middle one, to the center of the right monitor. This is so windows can be opened on the desktops outside game display.
I have two 8800s, and a MB that has two pci 2.0 x16 slots. Using one card and two monitors (two outputs from one card), I get good framerates.....40s to 50s. If I install the other card for a third output...to third monitor, my framerates for all are cut about in half...20s or below.
On this MB, apparently, when two cards are used, the pci x16 slots become x8 slots. Also, this MB has crossfire, and I have nvidia cards. I wonder if either of these facts are the cause of the massive lowering of framerate going from one card to two.
Or is it an additional strain on the cpu to have two cards?
Would it help to have a MB that provides pci 2.0 x16 on two slots if two cards are used?
To be clear, this is not a sli setup. The two cards are being used to provide enough outputs for three monitors.
Has anyone tried a setup like this before? Any help would be greatly appreciated, thanks:)

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huron   08-27-2008 at 12:29:29 AM
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I believe the fact that you are using half the bandwidth per card should affect the performance significantly (like you've seen). I believe that if your motherboard had full x16 2.0 slots, you wouldn't see this issue (or so significantly).

Can you give specs so we can further help you. Do you have a P35/P45?

I was thinking of doing a similar setup - mine would be one gaming monitor, 2 for work/fun.

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judgedee   08-27-2008 at 12:44:21 AM
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ASUS P5Q-E LGA 775 Intel P45 ATX Intel Motherboard
Sorry, should have given more specs....this has p45 chipset
Cpu is an Intel Quad at 2.66
Monitors are 3 matching 26" lcds


Message edited by judgedee on 08-27-2008 at 01:31:05 AM
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taso11   08-27-2008 at 02:45:13 AM
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I had been trying to get three monitors to work on my gaming pc but nothing worked right. I have 3 8800gtx's in tri sli and 3 23" HP monitors. Sure I could get a super wide desktop while not in sli. But that's not what I was going for. I bit the bullet and bought Matrox's Triplehead2go digital. Now everything works the way I wanted. For driving sims it ok but if you're playing shooters, 3 monitors is a lot to keep track of!

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dagger   08-27-2008 at 02:53:06 AM
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It could be the 8x pcie bandwidth, considering how badly 4850 cf is bottlenecked by it.
http://www.tweaktown.com/articles/ [...] index.html

If you just brought the 8800s, instead of them being leftovers, consider returning them for a single non-reference card that supports 3 monitors. This 3870x2 supports 4 monitors, cost $220 ar. While it's old, it still performs on par to a single 4870 while costing less.
http://www.newegg.com/Product/Prod [...] 6814121247

------------------------------ Q6600@3.6ghz, GA-EX38-DS4 motherboard, 8gb 800mhz ddr2 4-3-3-12, 8800GTS(g92)@780mhz, 1TB + 1.5TB hdds, 850watt psu
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taso11   08-27-2008 at 03:11:42 AM
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I forgot about your bandwidth issue. I am not familiar with your motherboard but some allow you to select pci express bandwidth in the bios. You can run 3dmark06 with different pcie settings either 8x or 16x and see if that is restricting your cards. Or it could be that there is more overhead from the two video cards trying to communicate with each other on a motherboard that was optimized for crossfire. Stuff to think about.


Message edited by taso11 on 08-27-2008 at 03:12:31 AM
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