In Theory: How Does Lynnfield's On-Die PCI Express Affect Gaming?

Four Architectures, Four Chipsets, Tons Of Variables, Continued

Core 2 Quad

Ah, the lineup Core i5 will purportedly be replacing. We went with Intel’s Core 2 Quad Q9550, running at 2.83 GHz (as close as we could get to a stock 2.8 GHz using the 1,333 MHz bus setting). Hopefully, this will make for one of the most apt comparisons to Core i5, since the price points should be similar and P45’s 16 lanes of PCIe 2.0 also result in a x8/x8 split when you install two graphics cards. What’ll be left is the performance delta attributable to Intel’s micro-architecture shift.

Intel Core 2 Quad @ 2.83 GHz
Socket Interface
LGA 775
Chipset
Intel P45
PCI Express Configuration
1 x 16-lane, 2 x 8-lane
Core Configuration
Four physical cores, four threads (no HT)


As mentioned, we’re going with P45 on this one. We could have chosen X48 and enjoyed two x16 links, but 16 lanes total is what Core i5 brings to the table, and that made for the most sensible comparison.

Intel P45Intel P45

Phenom II

Remember that our performance look here is largely an exercise in theory. Because we’re using pre-production hardware, we’re not looking to recommend one platform over another at this point. You'll want to look at the Core i5/Core i7 review for that one (fortunately, also published today). With that said, we used an AMD Phenom II X4 920, running at 2.8 GHz to match the clocks of our other contenders.

The least-expensive chip in the bunch at $190, we’ll go into more on pricing and what it means to the overall value picture later in this story. For now, we’re most concerned with how these 2.8 GHz processors perform given different designs and PCI Express configurations.

AMD Phenom II X4 @ 2.8 GHz
Socket Interface
Socket AM2+
Chipset
AMD 790GX
PCI Express Configuration
1 x 16-lane, 2 x 8-lane
Core Configuration
Four physical cores, four threads


As with the Core 2 Quad configuration above, we could have gone with AMD’s 790FX chipset here, yielding a pair of x16 links. But the more mainstream/sensible choice is 790X or 790GX, which takes a single x16 link and divides it up into two x8 links when you drop in a pair of similar Radeons.

AMD 790GXAMD 790GX

Again, this gives us a good basis for comparison to P55 and P45, the other two platforms equipped with dual-x8 links.

Graphics

For the purposes of testing both single- and dual-card solutions, we’re using ATI’s Radeon HD 4870 X2—the fastest card you can buy able to run in CrossFire on all four of these motherboards (in comparison, SLI only works on the X58 and P55 boards).

Twin Radeon HD 4870 X2sTwin Radeon HD 4870 X2s

We’ll test all four of the setups with one card, yielding performance numbers for 16 lanes of second-gen PCI Express 2.0, and then with two cards, ideally demonstrating bottlenecks in running these fast cards in x8 slots, processor bottlenecks, or maybe even solid scaling (spoiler alert: it’s a fairly safe bet that, at 2.8 GHz, we won’t see four RV770 GPUs realize their potential—we’ll have to wait for a faster Core i5 in order to ratchet up processor speed).

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33 comments
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    Top Comments
  • megabuster
    AMD better have something up its sleeves or it's instakill.
    11
  • Other Comments
  • megabuster
    AMD better have something up its sleeves or it's instakill.
    11
  • rambo117
    AMD... your loosing your game...
    -1
  • dirtmountain
    A PhenomII x4 920? ouch
    9
  • bucifer
    I do not agree with the choices made in this article. You don't buy 2*4870x2 and the you slam a x4 920. The choices do not make sense.

    You should have used the best cpu(ex i7 920 oc@4GHz) to try to eliminate all bottlenecks and truly emphasize the limitations of x8/x16 pci-e lanes.

    The rest of the testing was done to include the new i5 which is not bad but not relevant for the bottleneck. I know many people would like to see how i5+p55 handles the gpu power but it's a highly unlikely scenario that someone would actually but such powerful and expensive cards on pair them with a cheaper cpu and a limited platform.

    I just think you should have tested things separately in different articles.
    -10
  • radnor
    I know you used a 2.8Ghz Deneb for Clock-per-clock comparisons. MAkes sense. But a 2.8 Ghz Deneb is something really no unlocked. Ussually unlock versions go 3.5Ghz on stock VID, non BE PArts can reach 3.3Ghz safely.

    A 2.8 Deneb/Lynnfield/Bloomfield have completely diferent prices. You are comparing a R6 vs a R1. I7 is the Busa trouting everybody else. Of course the prices are very diferent.
    1
  • cangelini
    Gents, if you want to see the non-academic comparisons, I have the 965 BE compared in two other pieces for more real-world comparisons!
    http://www.tomshardware.com/reviews/intel-core-i5,2410.html
    and
    http://www.tomshardware.com/reviews/core-i5-gaming,2403.html
    Thanks for the feedback notes!
    0
  • bounty
    "Will Core i5 handicap you right out of the gate with multi-card configurations? The aforementioned gains evaporated in real-world games, where Core i7’s trended slightly higher, perhaps as a result of Hyper-Threading or its additional memory channel"

    Well you answered will i5 handicap you without hyperthreading, x8 by x8 and dual channel. It will by 5-10% If you wanted to narrow it down to memory channels, hyperthreading or the x8 by x8 you could have pice the game with the biggest spread and enabled each of those options selectively. Would have been kinda interesting to see which had the biggest impact.
    3
  • Shnur
    Great article! But then again... I don't see why a 955 wasn't used in this scenario... since the 920 is thing that nobody uses. Already that we know that i7 is superior to AMD flagship in multi-GPU configurations you're taking a crappy AMD CPU, buying a 790GX doesn't mean you're going to cut on the chip... and you're talking about who's performing better in 8x lanes... from my point of view it's a bad comparison, and there should have been a chip that'll be actually able to take a difference between 1 card and two and the from 16x and 8x.
    And thanks for the other linked reviews, but I'm not talking about comparing the chips themselves, I'm trying to figure out is 8x still good enough or I need to pay more for 16x?
    -2
  • cangelini
    Shunr,
    Thanks much for the feedback--again, this wasn't meant to be about the CPUs, but the PCI Express links. If you want to know about the processors themselves at retail clocks, check out the gaming story, which does reflect x16/x16 and x8/x8 in the LGA 1366 and LGA 1156 configs.
    Hope that helps!
    Chris
    5
  • Shadow703793
    megabusterAMD better have something up its sleeves or it's instakill.

    lol! do you mean instagib?

    Joking aside, AMD needs something to counter this.
    2
  • Alkapwn
    There may be a slight flaw to your testing methodology on the i7 vs i5. You used an i7 975 against the i5 750. You clocked the CPUs to the same, 2.8 Ghz, but made no mention of the uncore speed. Uncore clock of the i7 975 runs @ 2.66 Ghz, whereas the i5 750 runs @ 2.16 Ghz. Since the PCI controller on the i5 is part of the uncore, answering the question "How Does Lynnfield's On-Die PCI Express Affect Gaming" against the i7 975 will only show skewed, or dare I say flawed, results.

    If you're going to make an *apples to apples* comparison, the i7 920 would have been a better choice, as its uncore is clocked the same as the i5, and both run their cores at the same stock speeds. This would have presented a level playing field in both processor speed as well as uncore speeds.

    Thank you.
    4
  • CookYouAll
    Sad, AMD losing again, again & again..
    -3
  • tkgclimb
    Why did they use a 790gx platform not a 790fx, doesn't the FX have more pci-e bandwith, and does better supporting multi gpu configurations? or am I about to buy the wrong mobo.
    -1
  • rambo117
    tkgclimbWhy did they use a 790gx platform not a 790fx, doesn't the FX have more pci-e bandwith, and does better supporting multi gpu configurations? or am I about to buy the wrong mobo.

    did you read the whole article? its explained here:
    http://www.tomshardware.com/reviews/core-i5-lynnfield,2379-3.html
    1
  • tkgclimb
    rambo117did you read the whole article? its explained here: http://www.tomshardware.com/review [...] 379-3.html


    Yeah I read it, but it really doesn't make sense even though the i5 has only 16x bandwidth I don't think they should limit AMD to only 16x also.

    But good article,

    weird how the the PHenom scales so badly in crsfr still using the same amount of bandwidth as all the rest of the CPU's
    -2
  • spearhead
    i dont find it strange that PHII seems to scale alot less here. PHII was clocked back to 2,8GHZ otherwise the results would have been much more even when benched vs a stock clocked i5 750. This benchmark brings out the clock advantage of the architectures. But it dousn't smell like real world preformance to me. never the less scores above 60-75 FPS are above noticeble. fewer then that would also not hurt tough since a few frames are always being prerenderd. That is why i cannot justify I7 920 any longer for anything less then a multiple solution. never the less i5 750 is going to be priced quite near the PHII 955 just a few tens more expansive, with some luck AMD considers dropping the price a bit more. Over all I5 750 is a good awnser VS the phenom 955 and 965. And while both offer there own advantages such as intels clock advantage it would not run as near its physical limits as a stock phenom II dous whe your into overclocking. But AMD on the other hand is still a bit cheaper and will bring out a 6 core istanbul based 32nm cpu somewhere next year which will work on every current decent AM3 board. core i5 still be the current winner when your aim is to overclock
    0
  • Ciuy
    so it sucks
    -5
  • suitaoli
    what aboutthe Hyper threading in i7 Bloomfield benchmarks, disable or enable?
    -1
  • suitaoli
    suitaoliwhat about the Hyper threading in i7 Bloomfield benchmarks, is it disable or enable?
    -2
  • Anonymous
    so let me get this straight...you took two almost exactly the same architectures and ran tests where the extra bandwidth of the memory of one don't matter and where both had sufficient PCI bandwidth and you're shocked that they performed the same clock for clock? seriously? You guys are fucking geniuses!!! STOP THE FUCKING PRESSES TWO SIMILAR ARCHITECTURES PERFORM SIMILARLY should be the title of this article
    -5