Setting up a development machine, I was wondering about the way I should connect the displays. The machine has two monitors and also has two graphics cards (2x GeForce 9800 GTX+) both having 2 DVI ports. What I have been wondering is if it better to connect both monitors to a single card or one monitor to each card? Is one configuration definitively better then the other, and if not what would be the benefits & detractors of each?
Dual monitors with dual Graphics Cards
graphicshardware
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Well I had a theory about IRQ sharing, but you have identified it as a driver issue. I think it is likely that nVidia never expected someone to run dual PCI cards. They probably only account for PCI-Express + PCI or AGP + PCI.
Each PCIe (v1) lane should comfortably handle 2 x 1Gbe links.
At this point DDR2 can comfortably handle the data rate of 10Gbe.
In general the PCIe layout of a machine is dictated by the chipset, and if you can find a diagram from Intel or whoever you should be able to work out where any bottlenecks are.
For example:
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You don't say which OS or whether the two cards are in the same type of slot.
On Windows, a large virtual desktop spanning multiple monitors can be set up no matter which way you connect them in your circumstances. I don't have any multimon experience on Linux and I've forgotten what i knew about OS X.
Regardless of the OS, I would think that some operations that span the two monitors would have better performance if they stay on one card and don't involve the bus or the OS. So I would recommend that you use one card until you get more monitors.
However, performance depends on the particular combination of factors in a specific configuration. The OS, drivers, slot type(s), bus speed etc. all interact. The only way to tell for sure without doing a well-designed benchmark. I would find something that does a lot of OpenGL and displays the frame rate. Run it so that it spans the two monitors (if it will let you) and try it in each potential configuration.