PCI Express & CrossFire: Scaling Explored

Performance Summary And Conclusion

If this were a standard motherboard review, we might simply throw up a single chart to show the overall performance differences between various CrossFire configurations, and it would look like this:

But while the simplified chart does show the problem of running CrossFire on P35 and P965 Express chipsets, it doesn’t really address the needs of individual buyers. The biggest concern will be the level of detail and resolution each gamer requires to reach a gaming-immersion comfort level.

At our lowest settings, the average gamer is best-advised to use a single card.

Increasing visual quality levels while maintaining a low resolution puts emphasis on memory performance, not graphics performance, as indicated by a significant win for the 975X motherboard.

Most middle-market buyers use either an old 1600x1200 display or a more modern 1680x1050 wide screen. At low-quality settings, the CrossFire performance advantage is generally too small to call any upgrade a good value unless a specific game requires the added performance.

Anyone who likes their games to look good and has at least a medium-resolution flat panel will love the performance boost CrossFire gives to our more modern motherboard choices. On the other hand, x4 pathways for the secondary graphics slots of P965 and P35 Express motherboards make any CrossFire upgrade a bad idea overall.

CrossFire really shines at 2560x1600, but anyone who can afford a 30” flat panel probably wouldn’t settle for low-quality graphics details.

Increasing detail levels enables even more value on the CrossFire solution, but anyone who can afford a 30” flat panel probably isn’t in the market for old system upgrades. Thus, the X48 and P45 results should be the only ones that matter at these settings.

Conclusion

Upgrading CrossFire-ready chipsets with a second graphics card is a great way for gamers to extend the useful life of their systems, as it provides nearly universal performance increases at medium to high resolutions and high details. Huge gains found on chipsets as old as the 975X prove that age isn’t a problem for buyers seeking a moderate-cost system renovation. Unfortunately, many other users don’t realize that their chipsets aren’t suitable for a CrossFire upgrade, in spite of any second or third graphics card slots.

Individual benchmarks showed that CrossFire performance is far too inconsistent on P35 and P965 chipsets to recommend it universally. In fact, several benchmarks suffered significant performance losses due to the low bandwidth of the second graphics card slot. Owners of these ill-equipped motherboards must carefully consider which games they’d like to continue playing before taking the plunge.

The easy solution for P965 and P35 Express systems is to simply use a single, more powerful card. At the very least, the issue we encountered where a secondary PCI Express x4 slot’s limited bandwidth hurt performance can be avoided by using a single card, so comments such as "CrossFire doesn’t work right" wouldn’t apply to single-card CrossFire solutions such as the HD 4870 X2. But the point of this article was to judge the viability of adding a second card when a reasonably good card is already installed, and this is an area where P965 and P35 Express motherboards simply cannot be upgraded to compete with modern builds.

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96 comments
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  • badge
    Thanks for laying that information out.
    2
  • sparky2010
    should've included 1920x resolutions in the last page, as there are a lot of people out there with screens capable of that resolution.. but anyways, all in all a very good and informative article.. but i'm going to settle with a complete makeover when core i7 becomes more available!
    5
  • V3NOM
    yer kinda interesting to see how things have changed with new mobos but it doesnt really have any practical value tbh.
    -1
  • Crashman
    V3NOMyer kinda interesting to see how things have changed with new mobos but it doesnt really have any practical value tbh.


    It's all about answering the question "Will a second card do the job".

    Lots of guys have midrange or better ATI graphics cards, and the question of "upgrade or replace" is constantly being asked.
    5
  • outlw6669
    Thanks for finally getting this review out!
    0
  • arkadi
    p45 looks grate, and the price is right.
    1
  • arkadi
    btw x58 is out there, just a reminder.
    -9
  • outlw6669
    @ arkadi
    Yes the x58 is out.
    However, as it can not be paired with a Core 2 CPU and runs DDR3 exclusively, you can not directly compare the results.
    In general, I would assume crossfire on the x58 will scale similarly to the x38/48 as they both have the same PCIe configuration.
    1
  • Crashman
    outlw6669Thanks for finally getting this review out!


    It was planned for September but kept getting delayed due to tight deadlines on other articles. But when the economy finally went from a slow decline to a nosedive in November, we knew this article had to come out right away. More people are putting new systems on hold and looking for ways to keep their old ones up to current performance standards, and we care about upgraders just as much as system builders.
    2
  • arkadi
    Yeah I know, the comment was in general...
    -1
  • dimaf1985
    great article. consise and informative at the same time. now if only there was one for amd chipsets...
    0
  • Anonymous
    toms...i have loss so much respect for this website...stuppes
    -17
  • marraco
    Good work!.

    Altought, I have an Athlon X2 system, and probably gonna update to a I7 920. It would had be better comparing to an cheap i7 as a reference
    0
  • Lurker87
    Excellent info. It'll be nice having this article to link to.
    1
  • antiacid
    This article shows that even in the best conditions, x48 vs p45 is at most 5% difference. Price-wise, this confirms my observations that the lower priced P45 boards are much better performance/value than the x48 premium counterparts.
    5
  • Roland00
    I understand it is more testing, and you already had several months of delays but it would have been nice to see 1920x1200 numbers. 24" monitors are now in the mainstream affordability range with prices ranging from $249 to $349
    2
  • waffle911
    I might be missing something, but it kinda looks like a Phenom 9950 paired with the 790FX SB750 would be comparable to the X48. But really, what am I missing? I can't find a direct comparison anywhere.
    1
  • waffle911
    Sorry: bit of an oversight on my part. CPU charts of course, though the AMD board is using the older SB600, but the performance difference shouldn't be much different.
    0
  • Crashman
    Roland00I understand it is more testing, and you already had several months of delays but it would have been nice to see 1920x1200 numbers. 24" monitors are now in the mainstream affordability range with prices ranging from $249 to $349



    You're right! The problem is trying to test a whole bunch of different resolutions. 1920x1200 is almost right in the middle between 1680x1050 and 2560x1600, so hopefully most people can figure out "about" where that resolution would fall on the charts.

    Is it time to get rid of 1024x768? I'm in favor of ditching that resolution and picking a different one.
    2
  • FlorinR
    I'm trying to figure out something after reading this article, maybe someone could help me understand??? It seems that a SINGLE Radeon HD 4870 still have enough bandwidth into a PCI-E 1.1 slot, and the differences in performance compared to PCI-E 2.0 came from the chipset (P35 vs. P45 in SINGLE card configuration). Am i wrong?
    0