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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 InterfaceLGA 775
ChipsetIntel P45
PCI Express Configuration1 x 16-lane, 2 x 8-lane
Core ConfigurationFour 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 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 InterfaceSocket AM2+
ChipsetAMD 790GX
PCI Express Configuration1 x 16-lane, 2 x 8-lane
Core ConfigurationFour 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.


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


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 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).

Chris Angelini is an Editor Emeritus at Tom's Hardware US. He edits hardware reviews and covers high-profile CPU and GPU launches.