Please explain crossfire/2 GPUs

[cly]

I am being a little lazy and don't want to read an entire encyclopedia. Could someone explain why you would use 2 GPUs. I have a radeon 4850. It has two DVI outs. Which means I could hook this up to two independent monitors. right? If I had two card then I would have four DVI outs. Do you need 2 cards in case you require high performance for your graphics? Using one card would freeze/not work? Do you then just use 2 of the 4 outputs? Is the alternative getting a very high performance GPU instead of using two lower performance GPUs? Any clarification would be great. Thanks

 

[MatTheCat]

I am being a little lazy and don't want to read an entire encyclopedia. Could someone explain why you would use 2 GPUs. I have a radeon 4850. It has two DVI outs. Which means I could hook this up to two independent monitors. right? If I had two card then I would have four DVI outs. Do you need 2 cards in case you require high performance for your graphics? Using one card would freeze/not work? Do you then just use 2 of the 4 outputs? Is the alternative getting a very high performance GPU instead of using two lower performance GPUs? Any clarification would be great. Thanks

I have never ran a CF configuration. But the general idea is that you hook the two cards up with a CF bridge (supplied with ATI cards) and the two run as one which can provide much better performance in many games. You would indeed just be able to use the two, instead of four outputs, either to use one as extended monitor or clone monitor.

 

[cly]

So I guess the only reason to do this is if I started running into problems having dual monitors with just the one card.

 

[DirectorC]

People used to do it before there were cards with dual-GPUs and all cards were relatively weak. People still do it as an upgrade path (if they can only upgrade one somewhat weak card at first, but plan to upgrade later, many go for Crossfire/SLI).

You could spend under $100 just adding another 4850 in Crossfire and get some great performance out of it, or you could sell your card and buy a 5800 series card.

But the first two sentences basically describe why SLI/Crossfire exist.

 

[cadaveca]

I have a radeon 4850. It has two DVI outs. Which means I could hook this up to two independent monitors. right?

Yes, 4850, 2x dvi, 2x monitors at the same time.

If I had two card then I would have four DVI outs. Do you need 2 cards in case you require high performance for your graphics?

With 2 4850's, you'll get a performance increase, needed for some games @ some resolutions, with certain settings. How much performance is dependant on the rest of your system.

Do you then just use 2 of the 4 outputs?

You can also use many videocards for many monitors, but when the gpus are working together in 3D, only the outputs of the main card are usable. You can link up to 4 cards of the same model in Crossfire.

Is the alternative getting a very high performance GPU instead of using two lower performance GPUs?

Crossfire can be used as en easy upgrade path, or simply to increase performance. The 5-series can run up to 6 monitors at once from one card, and to do 3D on so many monitors requires quite a bit of power...more than any one card could provide, given average graphical settings.

I'm running 3x 23-inch 1920x1080 monitors together, with 2 cards, using 2x 5870. 1x 5870 was not fast enough, and I'm finding that for the performance I desire, I'm going to need at least a third gpu, but that seems right to me, with three monitors.

 

[cly]

The 5-series can run up to 6 monitors at once from one card,

How could you hook up three monitors two one card if the card only have two outputs? are two of the monitors clones?

 

[cadaveca]

No, the 5-series card in reference form have 2xDVI, 1xHDMI, and 1xDisplayport. The HDMI is linked to DVI, so if you use HDMI, you lose one DVI port, but one card alone supports 3 monitors. This is refered to as "Eyefinity" by AMD/ATI, as it allows Windows to see the monitor as one single panel, allowing for 3D across all three monitors.