Graphics is infinitely parallel. There is always more work that can be done, and the work can be broken up into millions of completely independent operations. This is very different than most tasks we see done on the CPU that don't scale quite as easily with the number of cores. While we might see small improvements by adding another CPU, we can see nearly double the performance by doubling the number of processors in a graphics card (as long as there are no other bottlenecks anyway). This fact is why AMD and NVIDIA have invested so much money into their respective multiGPU solutions (CrossFire and SLI respectively).

MultiGPU solutions have been around for a few years now, and while we frequently include single card multiGPU solutions in our reviews, we only occasionally take an in depth look at multiGPU technology. Some time has passed since the last time we studied the issue, and now that we've fully broken in our Core i7 system, 64-bit Vista, and recent graphics drivers, it's time to get to it.

Over the past few weeks we've been benchmarking and analyzing lots of numbers. We've looked at single, two, three and four GPU systems across multiple games and resolutions. The configurations we chose to look at are current generation high-ish end hardware capable of operation in 3-way and 4-way configurations. Because of the sheer volume of data we collected, we've decided to break up our analysis into multiple articles.

This first article (the one you're reading right now) will cover single and dual GPU configurations (including single card multiGPU hardware). The next article will add 3-way solutions along with comparisons back to single and dual GPU setups. The final article will add in 4-way performance analysis and compare it back to the single, dual and 3-way data. Splitting up the analysis this way will allow us to dive deep into each type of configuration individually without spreading the content too thin. We can keep focus on a specific aspect of multiGPU performance and scaling while still making all the relevant comparisons.

The initial installment also introduces the Sapphire Radeon HD 4850 X2 2GB. Though we expected AMD to push the 4850 X2 out in the same way they launched the 4870 X2, we've only seen one version of the 4850 X2 hit the scenes late last year from Sapphire. In light of what we've seen, we are rather surprised that we haven't seen more fanfare behind this part from either AMD or other board makers. The lighter weight X2 competes more directly in price and performance to the GeForce GTX 280/285, and really fills out the lineup for AMD. Overall, the increased RAM in the 4850 X2 2GB enables great performance scaling even at resolutions the 512MB 4850 can't come close to handling.

As for the topics we'll cover, our interest will focus on scalability of the multiGPU solutions and the relative value of the same. Before jumping into the numbers, we'll cover the metrics we use to analyze our data. First, we'll look at scaling and talk about the big picture. Then we'll talk about what we've done to calculate a value comparison.

Who Scales: How Often?
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  • SiliconDoc - Wednesday, March 18, 2009 - link

    Oh, I'm sorry go to that new technolo9gy red series the 3000 series, and get that 3780... that covers that GAP the reds have that they constantly WHINE nvidia has but DOES NOT.
    Yes, go back a full gpu gen for the reds card midrange...
    GOOD GOLLY - how big have the reddies been lying? !?
    HUGE!
    Reply
  • MagicPants - Monday, February 23, 2009 - link

    I know you're trying to isolate and rate only the video cards but the fact of the matter is if you spend $200 on a video card that bottlenecks a $3000 system you have made a poor choice. By your metrics integrated video would "win" a number of tests because it is more or less free.

    You should add a chart where you include the cost of the system. Also feel free to use something besides i7 965. Spending $1000 on a CPU in an article about CPU thrift seems wrong.
    Reply
  • oldscotch - Monday, February 23, 2009 - link

    I'm not sure that the article was trying to demonstrate how these cards compare in a $3000.00 system, as much as it was trying to eliminate any possibility of a CPU bottleneck. Reply
  • MagicPants - Monday, February 23, 2009 - link

    Sure if the article was about pure performance this would make sense, but in performance per dollar it's out of place.

    If you build a system for $3000 and stick a $200 gtx 260 in it and get 30 fps you've just paid $106 ($3200/30fps)per fps.

    Take that same $3000 dollar system and stick a $500 gtx 295 and assume you get 50 fps in the same game. Now you've paid just $70($3500/50fps) per fps.

    In the context of that $3000 system the gtx 295 is the better buy because the system is "bottlenecking" the price.
    Reply
  • OSJF - Monday, February 23, 2009 - link

    What about micro stuttering in MultiGPU configurations?

    I just bought a HD4870 1GB today, the only reason i didn't choose a MultiGPU configuration was all the talkings about micro stuttering on german tech websites.
    Reply
  • DerekWilson - Monday, February 23, 2009 - link

    In general, we don't see micro stuttering except at high resolutions on memory intensive games that show average framerates that are already lowish ... games, hardware and drivers have gotten a bit better on that front when it comes to two GPUs to the point where we don't notice it as a problem when we do our hands on testing with two GPUs. Reply
  • chizow - Monday, February 23, 2009 - link

    Nice job on the review Derek, certainly a big step up from recent reviews of the last 4-5 months. A few comments though:

    1) Would be nice to see what happens and start a step-back, CPU scaling with 1 GPU, 2 GPU and 3 CPU. Obviously you'd have to cut down the number of GPUs tested, but perhaps 1 from each generation as a good starting point for this analysis.

    2) Some games where there's clearly artificial frame caps or limits, why wouldn't you remove them in your testing first? For example, Fallout 3 allows you to remove the frame cap/smoothing limit, which would certainly be more useful info than a bunch of SLI configs hitting 60FPS cap.

    3) COD5 is interesting though, did you contact Treyarch about the apparent 60FPS limit for single-GPU solutions? I don't recall any such cap with COD4.

    4) Is the 4850X2 still dependent on custom drivers from Sapphire? I've read some horror stories about official releases not being compatible with the 4850X2, which would certainly put owners behind the 8-ball as a custom driver would certainly have the highest risk of being dropped when it comes to support.

    5) Would've been nice to have seen an overclocked i7 used, since its clearly obvious CPU bottlenecks are going to come into play even more once you go to 3 and 4 GPU solutions, while reducing the gain and scaling for the faster individual solutions.

    Lastly, do you plan on discussing or investigating the impact of multi-threaded optimizations from drivers in Vista/Win7? You mentioned it in your DX11 article, but both Nvidia and ATI have already made improvements in their drivers, which seem to be directly credited for some of the recent driver gains. Particularly, I'd like to see if its a WDDM 1.0-1.1 benefit from multi-threaded driver that extends to DX9,10,11 paths, or if its limited strictly to WDDM 1.0-1.1 and DX10+ paths.

    Thanks, look forward to the rest.
    Reply
  • SiliconDoc - Wednesday, March 18, 2009 - link

    Thank you very much.

    " 2) Some games where there's clearly artificial frame caps or limits, why wouldn't you remove them in your testing first? For example, Fallout 3 allows you to remove the frame cap/smoothing limit, which would certainly be more useful info than a bunch of SLI configs hitting 60FPS cap.

    3) COD5 is interesting though, did you contact Treyarch about the apparent 60FPS limit for single-GPU solutions? I don't recall any such cap with COD4.

    4) Is the 4850X2 still dependent on custom drivers from Sapphire? I've read some horror stories about official releases not being compatible with the 4850X2, which would certainly put owners behind the 8-ball as a custom driver would certainly have the highest risk of being dropped when it comes to support.
    "

    #2 - a red rooster booster that limits nvidia winning by a large margin- unfairly.
    #3 - Ditto
    #4 - Ditto de opposite = this one boosts the red card unfairly

    Yes, when I said "red fan boy" is all over Derek's articles, I meant it.
    Reply
  • DerekWilson - Monday, February 23, 2009 - link

    thanks for the feedback ... we'll consider some of this going forward.

    we did what we could to remove artificial frame caps. in fallout 3 we set ipresentinterval to 0 in both .ini files and framerate does go above 60 -- it just doesn't average above 60 so it looks like a vsync issue when it's an LOD issue.

    we didn't contact anyone about COD5, though there's a console variable that's supposed to help but didn't (except for the multiGPU soluitons).

    we're looking at doing overclocking tests as a follow up. not 100% on that, but we do see the value.

    as for the Sapphire 4850 X2, part of the reason we didn't review it initially was because we couldn't get drivers. Ever since 8.12 we've had full driver support for the X2 from AMD. We didn't use any specialized drivers for that card at all.

    we can look at the impact of multithreaded optimizations, but this will likely not come until DX11 as most of the stuff we talked about requires DX11 to work. I'll talk to NVIDIA and AMD about current multithreaded optimizations, and if they say there is anything useful to see in current drivers we'll check it out.

    thanks again for the feedback
    Reply
  • chizow - Monday, February 23, 2009 - link

    Oh and specifically, much better layout/graph display with the resolution selections! :) Reply

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