Crossfire meets PCI Express 2.0 – More Lanes, More Frames?

Conclusion - Switch to PCI-Express 2.0 Yields no Improvement

Putting current graphics cards in a PCI-Express x4 slot basically verges on madness and incurs a performance hit of between 25 and 33 percent. Even if the motherboard in question were especially cheap, the card’s price/performance ratio is affected immensely. When using an x8 connection, performance also decreases, albeit only by 7 to 8 percent.

Our switch to the X38 chipset for Crossfire tests was overdue. The dual x16 connections improve performance by 6 to 7.7 percent on average, while optimized games such as Call of Duty 4 run nearly 20 percent faster. Looking only at games and resolutions that show a tangible performance boost, we saw an improvement of 12 to 15 percent on average.

Another thing we saw is that a dual x16 configuration is not as effective for Crossfire as a single x16 slot is for a single card. As mentioned above, a single card loses between 7 and 8 percent performance when operating in an x8 slot. Moving from an x8 + x8 setup to an x16 + x16 connection also only yielded a 7.7 percent frame rate increase, though, and not twice as much, which we would have expected based on the single card results.

For now, the move from PCI-Express 1.0a to 2.0 does not result in a performance increase with the current crop of graphics cards. Despite the fact that it doesn’t feature the PCIe 2.0 interface ATI’s Radeon HD2900 XT gains two percent more performance, as do the HD3850 and HD3870 as well as Nvidia’s Geforce 8800 GT. Such a small improvement could have many causes completely unrelated to the new interface, such as the newer chipset, slightly higher system memory frequency or simply margin of error.

Whether or not upgrading to a P35 or X38 based motherboard is a worthwhile investment for a single-card system is a matter of personal preference. If you’re building a new system from the ground up, we would recommend choosing an X38 board with dual x16 connections for a Crossfire setup. Upgrading a Crossfire system from an Intel 975X or P35 chipset to an X38 will only pay off if you play at resolutions of 1920 x 1200 or above.

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  • strangestranger
    all very nice but like every article before this one, you do not mention the causes of bandwidth uses. so, like all your previous article's here on toms it is absolutely useless for anything other than saying"ooh, look at the fancy graph, aint they pretty" because apart from graphs the article has damn all to do with testing anything.
  • Tom_Smart
    I found it useful, I now know I can save money by not upgrading just yet. That's more beer money in my pocket, that has to be useful.
  • Mugz
    What I have, serves my needs. Besides, these articles tend to be aimed at the games-playing mentally-preadolescent set, so they can't get too in-depth.
  • drmouse
    Erm.. am I missing something?

    If one card increases by about 7% going from x8 to x16, then each card in a crossfire setup would increase by about 7% going from 2x8 to 2x16. Therefore the overall performance would improve by 7%. Why would you expect it to increase by more ("twice as much, which we would have expected based on the single card results")? If anything it should increase by less, due to increased loads on the chipset/system memory/processor etc.