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


There’s a ton of benchmark data here, from which we’re able to draw a number of different conclusions. But first, let’s revisit the questions posed in the introduction:

What’s this new design element going to mean to gamers? Will Core i5 handicap you right out of the gate with multi-card configurations? Remember, most P55-based platforms will support CrossFire and SLI. So, are eight lanes per card enough? How will P55 compare to X58, P45, and 790GX?

  1. How does incorporating 16 lanes of PCI Express 2.0 onto the Lynnfield die affect performance? The answer depends on how many graphics cards you’re using, but is mostly academic with this generation of GPUs. The more pressing concern should be finding a Core i5 that’s fast enough to actually let modern graphics cards stretch their proverbial legs. It all goes back to the concept of building balanced PCs. If you’re going to spend close to a grand on 3D horsepower, you’ll need a heavily-overclocked processor in order to keep pace. With a single Radeon HD 4870 X2, we saw some theoretical advantages to serving all 16 lanes through an on-die controller versus using X58.
  2. 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. With two cards installed, Core i5 simply didn’t gain as much performance as Core i7 at high resolutions. It wasn’t, however, noticeably handicapped, and was still able to deliver more performance than Core 2 Quad (also limited to a pair of x8 connections via P45).
  3. Are eight lanes per card enough? Almost certainly, yes…in this story. There is a perceivable performance ding associated with halving PCI Express bandwidth when two cards are installed. However, if you flip over to our Core i5 and Core i7 gaming analysis, which tests these two new chips with Turbo Boost turned on, you'll see that in most cases, the higher clocks measured there are able to make up some of the losses at low resolutions, while high-res tests demonstrate very close performance between the mainstream P55 platform and higher-end X58-based configurations.
  4. How will P55 compare to X58, P45, and 790GX? Naturally, X58 has an advantage in that it’s able to serve up twin x16 links and communicate with the CPU across a 25 GB/s+ QPI interconnect. P55, P45, and 790GX all force you to split connectivity up unto smaller links if you run multiple graphics cards, though. Integrating that functionality into the processor die looks to be a good thing for Core i5, especially given the motherboard/processor prices we're expecting immediately after launch.

Of course, this story doesn’t wrap up quite that simply. There’s still the matter of cost. For the price of a Core 2 Quad Q9550 at 2.83 GHz, you could actually buy a Phenom II X4 955 Black Edition at 3.2 GHz. The Core i5-750 is launching at $199, though, on motherboards priced as low as $100 in many cases. You're crazy if you think this won't cause a major shakeup in pricing, both for AMD and Intel, which will only be measurable after the platform proliferates post-launch.

For the time being, we're comfortable making the following observations:

Clock for clock, Core i5 is going to give you better gaming performance than Core 2 Quad. Because Core i5-750 is launching below the price of Core 2 Quad Q9550, this makes the story even sweeter. Core i7 for LGA 1366 does have an advantage in its QPI link to the X58 chipset, which offers high-end graphics cards full x16 PCI Express links. However, current-generation GPUs still deliver compelling performance over the x8 links enabled through P55, P45, and 790GX running in CrossFire mode. Finally, for games not optimized to take advantage of Core i5's four cores, we expect Lynnfield's Turbo Boost implementation to have a bigger impact on gaming performance than Bloomfield's.

As an aside, the benchmarks we saw in the previous pages make it painfully clear that if you want to run multi-card configurations with high-end graphics boards, be darned sure you have the platform to back them up. In many cases, that'll mean moderate CPU overclocking. Fortunately, we have something for you there, as well...

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