PCIe x16 slot speeds?

[Zemfik]

Can someone explain to me what it means for dual PCIe x16 slots to have one at x16 and another at x4 (or x8, or whatever)? What exactly does this affect? Is it much worse than having them run both at x16? Is the X38 chipset the only one that supports both at x16?

Thanks.

[patrick5432]

When it says it's 16X+4X, that means the second slot is physically the size of a 16x PCIe slot, but is electrically only a 4X PCIe slot. Crossfire takes a signifigant hit using it, but still performs relatively well.

X38 is the only Intel platform chipset that supports both lanes at 16x for Crossfire. The 680i and 780i boards support dual 16X on the Intel platform, but are SLI only.

For AMD platforms, there are a few chipsets that support dual 16X.
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