MB + CPU for 2 GPU System

I plan to build my own Intel based system that can support 2x GPU’s. My assumption is that it would be wise to have a system capable of operating at least 32 lanes of 3.0 PCIe. So far, I haven’t found an 1150 socket CPU that can support more than 16 lanes. It seems odd then, that there are a multitude of 1150 socket MB’s on the market that have 3 or 4 (or more) PCIe 3.0 x16 slots. I think this means that using 2 slots restricts each to operate at x8 electrically, or x4 if 4 slots were used.

Based on the above, it seems to me socket 2011 is pretty much mandatory to avoid potential bottlenecks.

Is my understanding correct?

Now I’m really confused. I just looked at an 1150 MB with 5 PCIe x16 slots and the specs say:

5(x16 or dual x8 or x8/x16/x8 or x8/x16/x8/x8)

The x16 or dual x8 makes sense, but the x8/x16/x16 adds up to 32 lanes and x8/x16/x8/x8 adds up to 40 lanes. I don’t see how can this be for a CPU that can’t support more than 16 lanes.

What am I not correctly understanding?

This is not my area of expertise, but I am aware that there are some non-server CPUs that offer 40 PCIe lanes, such as Core i7-5930K. From what I can tell, they all require a X99-based socket 2011 motherboard.

You might want to consider whether the GPU-accelerated application(s) that you plan to run on this dual-GPU system are actually bottlenecked by PCIe throughput. In my experience few GPU-accelerated applications fall into that category.

What I still don’t get is how a MB manufacturer (1150 socket) will produce a board with four x16 slots and claim 40 lanes are supported when the CPU is only capable of 16 lanes. There is something I’m not properly understanding. I wonder if maybe SLI muddies the water enough to allow the 40 lane claim when in fact only 16 are used?

Have you considered the possibility that the description you read could contain an error? Have you tried contacting the manufacturer / vendor for clarification?

Have you considered that there are PCI express bridge chips that motherboard vendors sometimes put on their motherboards to provide additional PCIE slots/connectivity?

For example, this Asrock 1150 Mobo:

http://www.asrock.com/mb/intel/z97%20extreme9/

says:

“PLX PEX 8747 is a PCIe Gen3 bridge chip that offers solid PCIe 3.0 lanes for PCIe devices and is optimized to support high performance graphics. With the bridge onboard, this motherboard is able to support up to four VGA cards with 4-Way SLI or 4-Way CrossFireX at PCI-E Gen3 x8/x8/x8/x8 mode”

Ah, that could be the missing link. I now remember hearing a computer store salesperson mentioning something about MB bridge chips. Must be some sort of multi-plexing going on. He also said there was no graphics card on the planet that could saturate 8 lanes of 3.0 PCIe. Not sure I believe that one (unless he said 16 lanes, I really don’t remember).