Widescreen Gaming Forum

First of, the question:

As topic says, how is it handled.

1) Does the GPU(s) treat it as one huge resolution which is updated and then divided and sent to each monitor?
2) Does the GPU(s) do the calculations as for a 1920*1080 resolution x3 ?

The background

The need for more VRAM on the GPU goes up as the resolution goes up and as textures/AA etc are higher more detailed. There are a lot of benchmarks out today were you see a large performance drop when you have a higher resolution then 1920*1080, for instance 2560*1400. I would also guess that the drop is not proportional with the increase in resolution. Its like you have a smaller drop as resolution increases until you pass a line were the performance drop goes through the floor.

Without knowing, if the GPUs handle this as one huge resolution, like in example 1 above, which would be equal to playing on one huge monitor with a resolution of 5760*1080, i would bet the performance drop would be insane.

This leads me to the main issue, i have a 2x5970 quadfire setup (4 GPUs on 2 cards) with 2 GIG VRAM per card, that is 1 GB per GPU. If eyefinity is treated as example 1 above, i think the setup 2x5970 will be able to handle most games in eyefinety, and the "lack of" 2 GB VRAM will not be an issue. Basically, you have 4 GPUs which will have to cooperate with calculating 3x 1920*1200 resolutions in parallel.

However, if case 2 is true, then you may have a larger problem, since its only 1 image calculated with a resolution of 5970*1080, and the cooperation between the GPUs may not be so good.

The GPU just sees it as one large area to render to, and 1GB is only just enough for most games so long as AA is off and settings aren't on max. The fact it is one large area rather then 3 smaller ones does not change the fact it needs more memory to process the scene.

Bare in mind you may have 4GB total but that is 1GB per core, and the data is cloned between all 4, so you only have 1GB available to render, regardless of crossfire or screen setup. Multi GPUs render normally by a process called alternate frame rendering, this means each GPU takes it in turn to render each frame and must have a full copy of all the data needed to render in the memory connected directly to it.

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: ) Skid : )
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"Imagination is the only weapon in the war against reality."

Thank you for a very good and precise answer Skid :)

Think i finally decided to replace the 2x5970 with a 6990. 2x5970 beats a single 6990 on most benchmarks today, but i guess a 6990 is more then sufficient for eyefinity on todays games, and for the long haul, the 6990 will last longer, especially when the prices drop so i can add a 2nd 6990.

PS! if the prizes drop....didnt for the 5970 :)

Not sure how well 2x 6990 is going to scale. That's 4x GPUs we're talking about. So far the least problematic Eyefinity Crossfire setup has been 2x GPUs. The drivers in the last year have been problematic as to which properly scale.

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Brad Hawthorne
Product Manager
Nthusim Pty. Ltd. | www.nthusim.com

I'm currently running 6970 x2. It seems to do a great job on most games at 5760 x 1080. Not sure what the cost per fps ratio would be if you went with 4 GPUs, but you may want to consider putting in a 6950 to effectively have 3x GPU.

Overall, I love having 3 monitors. Even when I don't play a game at 5760 x 1080 resolution, I always have 2 extra monitors to either watch Netflix and surf the web. It is pretty amazing and I can't see myself going back to having just 1. (Currently have 3x 27" Planar 60hz monitors. Only sucky thing about them is they are TN.)

Just a few things to consider,

Ninefingers