Z170 PCIe Exspansion Slots

Furanot

Commendable
Mar 18, 2016
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I've been planning to build a Skylake rig for some time now, but I'll sure be waiting for the Zen CPUs to arrive on the market. I just wonder, are there z170 mobos that support 20 pcie 3.0 lanes or more? Later down the line I will go Crossfire, while having a WiFi adapter needing 4 lanes.
 
Solution
Z170 will not support dual x16 speed cards, but will support them at dual x8 speeds, plus there are plenty of lanes for your x4 wireless adapter.
They do. Here's how it all shakes out.



Z170 Platform including CPU = Max 42 PCI-E 3.0 lanes (typically 17 shared with other devices like USB, SATA, NIC, 16 reserved for GPU)

Z170 chipset = 26 PCI-E 3.0 lanes, can be segmented in groups of x1/x2/x4 (17 typically shared with other devices like USB, SATA, NIC)

Intel CPU = 16 PCI-E 3.0 lanes, can be segmented in groups of x4/x8/x16 (almost exclusively used for GPU)

The thing with Skylake chipsets is that explaining all of this is a mouthful and hard to get across. In the article I linked there is an image of the chipsets HSIO lanes that diagrams how they can be segmented, what lanes are shared with what, etc. Study that, it should help to clarify what I am attempting to say.

The reason we cannot have x16/x16 multi-GPU configurations, is because the chipset is incapable of supporting more than an x4 connection to any device that connects directly to it. Only the CPU is capable of that, which bypasses the chipset entirely. This is mostly because the connection between the CPU and chipset is essentially limited to a PCI-E 3.0 x4 connection, and so anything greater than an x4 connection would be bottlenecked by the DMI 3.0 interconnect between the CPU and chipset.

This is not to say that if you have an M.2 SSD with a PCI-E 3.0 x4 connection and a GPU connected to the chipset via a PCI-E 3.0 x4 connection that you will necessarily have a bottleneck, as it will alternate between the two devices when transferring data, but it may have some negative side effects (increased latency).

If you are wanting to have a dual-GPU and dual-M.2 setup, you should be fine with most Z170 motherboards (you need to check them carefully), but if you were planning to add six SATA drives to that, you would probably end up disabling one of the M.2 ports.