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PCIe Scaling Summary

PCI Express And SLI Scaling: How Many Lanes Do You Need?
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While most games show only modest differences between various slot configurations, Call of Duty: Modern Warfare 2’s unusually high variance accounts for 20% of our benchmark totals.

Builders can expect an average performance loss of 8% when going from a x16 to a x8 slot. That could be an important consideration when using a platform that has a limited number of PCI Express lanes, such as an LGA 1156 platform in SLI mode. But before we move on to the SLI tests, let’s see what effect these configurations have on power, heat, and efficiency.

Dropping PCIe lanes can reduce power consumption, but not enough to matter to most high-end PC owners.

We wouldn’t expect a difference in heat simply from using a different slot, so we weren’t surprised to find that none existed.

Losing moderate performance without a similarly-sized reduction in power is a recipe for an efficiency disaster, since the calculation compares performance to power.

Now that we know to expect an 8% average performance loss when moving a single GeForce GTX 480 from a x16 to a x8 PCIe 2.0 slot, let’s see how that difference translates to SLI. Do we really need more than sixteen PCIe lanes to support two high-end graphics cards?

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