DDR4 dimm read throughput is about 20GB/s per dimm. PCIe 3.1 x4 is 16GB/s. I feel very comfortable claiming that these optane dimms will not reach 20GB/s of sustained performance.

The advantage here being latency (and thus single queue throughput)

> PCIe 3.1 x4 is 16GB/s

PCIe x4 is 3.94GB/s. PCIe x16 is 15.76GB/s.

> DDR4 dimm read throughput is about 20GB/s per dimm

Per channel, not per dimm. Two dimms typically go into a singular channel.

> The advantage here being latency (and thus single queue throughput)

Agreed

But pcie bus is shared with other cards. So 8 dimms is 8x faster than 8 pcie cards.

> But pcie bus is shared with other cards.

No, it's not, that's the whole point of pcie, and dimms share the memory bus anyway, so the whole point is moot.

Well, it depends. "True" pcie slots do not share the bandwidth, but depending on available CPU lanes, which is awfully few in the last years on Intel - 16 lanes in top of the line i7? thats one graphics card - the slots are switched to 8x/8x, 8x/4x/4x and so on when populated.

M.2 slots are a whole another story, they are usually connected to the chipset instead of CPU on desktop motherboards (and finding this information for any particular board is difficult). The chipset is connected with CPU through DMI, which equals to pcie 4x and this is shared with everything on chipset - satas, gigabit ethernet, usb 3...

Hmm. In that case never mind.