What means by PCI Express 3.0 x16 : 2 (x16/0 or x8/x8)

I see PCIe 3 x16 in boards as 2 (x16/0 or x8/x8), and in others 2 (x16/x8 or x8/x8) or 2 (x16/2 or x8/x8)
i can't understand that, can anyone explain that plz
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More about what means express
  1. Those are motherboards that support Crossfire/SLI.
    Those numbers mean that if only one GPU is used it will be running at x16 but if 2 GPUs are used they will be running at x8 each.
    Some motherboards allow x16 while on crossfire/sli and some allow you to use 3 or even 4 GPUs usually on x4 if I'm not mistaken
  2. Assuming LGA 1155 there's only 16 PCIe lanes to the GPU and x16/x0 or x8/x8 is the correct link speeds to the PCIe unless there's a secondary chipset i.e. 'PLX'. The MOBO's with x16/x0 + x4 or x8/x8 + x4 then (x4) are non-GPU PCIe lanes and only PCIe 2.0; LGA 1155 has a total of 24 lanes, 16 are GPU (PCIe 2.0 or PCIe 3.0) and 8 lanes to the chipsets in PCIe 2.0 only.
  3. Pci-e 3.0 has twice the bandwidth of 2.0, so a 4x slot has the same bandwidth of a 2.0 8x slot.

    So basically a 2.0 4x slot is fine and won't bottleneck any of today's video cards.
  4. RE: "...so a 4x slot has the same bandwidth of a 2.0 8x slot.."

    Any NON GPU slot is running PCIe 2.0 and not PCIe 3.0 -- it would be nice but for now it's as I stated:

    16 lanes are GPU (PCIe 2.0 or PCIe 3.0) x16/x0 or x8/x8
    8 lanes to the chipsets in PCIe 2.0 only ; so a x4 PCIe is 2.0.
    Exception is MOBO's with the PLX chipset {handful of high-end Z77's} x16/x0/x16/x0 (x16/x16), x16/x0/x8/x8 (x16/x8/x8), or x8/x8/x8/x8 funneled back to PCIe 3.0 16 lanes IF all sub-components are PCIe 3.0 compliant: Ivy Bridge CPU, PCIe 3.0 GPU (GTX 600 series/HD 7000 series), and a Z77 + PLX MOBO.
  5. I also didn't understand this...
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