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How does PCIE g4 handle pcie3 devices

Long post/question incoming:

With the new launch of third gen ryzen I find myself in a tough spot. My current workstation has a 1950x and I had thought that I would be able to put a Zen 2 processor in it back when I purchased it. Now with the new socket and AMD dropping 16 core chips from threadripper I’m having a hard time deciding what to do. I don’t really need the more cores that would come with the 3960x but I do think I need the PCIE lanes. I need 2 graphics cards in my workstation for VMs along with 40Gb fiber and a sas controller. To my understanding the 3950x only has 16 pcie lanes now. does anyone know how those lanes would be split when pcie gen 3 cards are inserted? Would a card that normally runs on 8x pcie g3 now only need 4 lanes on a pcie gen 4 system?

I would really like to upgrade since IPCs are a little low on the 1950x and NUMA can sometimes be a headache. Just wondering if anyone might be able to help

Unfortunately it doesn’t work that way. 8 lanes is 8 lanes, so your pcie 3.0 card would still use 8 lanes, and talk at pcie 3.0 speed. There’s no splitting going on at the slot.

That’s not to say you couldn’t probably find (in a few years?) a riser card that contained a pcie 4.0 switch and multiple 3.0 slots, turning x16 at 4.0 into 4 x8 at 3.0 for example. I would expect to see those risers popping up at the enterprise level soon enough.

Ye old Zen 1 and 1.5 threadrippers are still beastly workhorses, they have a ton of bandwidth but it’s hard finding an single application that takes advantage of that.


Well thank you for confirming what I had suspected. Looks like I’ll just have to stick with my current setup for the time being.