GPU over pci-e 3 x4?

[Lord_Karango17]

With all the new external gpu docks shown off at CES (as shown below) this year one thing I'm noticing is that they are hooked up via pci-e 3 x4.

 

 

Why does sli at pci-e x4 not work on desktops, when they appear to be working fine on these external desktop solutions?

[Morgan MLGman]

I believe it's equal to PCI-E 2.0 x8 which is completely fine to not bottleneck GPUs

[UMxMarky94]

it does IIRC Linus did a video on it a while a go, you just got to cut the slot to be open ended so it can fit

[Godlygamer23]

Are they actually using SLI?

[Lord_Karango17]

it does IIRC Linus did a video on it a while a go, you just got to cut the slot to be open ended so it can fit

Wait, sli works over x4? Why the move over to pci-e 3 if gpus can work fine on pci-e 1 x16

[Lord_Karango17]

Those aren't SLIed

Yes I know that. My question is why nvidia does not let you use the card if its running at x4. An example of that being when the bottom pci-e slot on the mobo is x4, and you need to sli.

[Lord_Karango17]

It appears that nvidia cards still work at x4, and can even function at pci-e 1 x4 (jesus), so I must have been mistaken in thinking that nvidia does not let you use the card if its in a x4 slot.

 

https://www.techpowerup.com/reviews/NVIDIA/GTX_980_PCI-Express_Scaling/6.html

[AMICLG]

Yes I know that. My question is why nvidia does not let you use the card if its running at x4. An example of that being when the bottom pci-e slot on the mobo is x4, and you need to sli.

Most boards allow PCI gen selection. So you could just put the board in 2.0 mode so it's x8 on the bottom slot which should work fine then.

[Litargirio]

so I must have been mistaken in thinking that nvidia does not let you use the card if its in a x4 slot.

 

You were not mistaken, Nvidia cards do refuse to work on x4 slots, as seen here:

https://youtu.be/rctaLgK5stA?t=5m23s

[Godlygamer23]

You were not mistaken, Nvidia cards do refuse to work on x4 slots, as seen here:

https://youtu.be/rctaLgK5stA?t=5m23s

My 660 Ti runs on a PCIe 2.0 x4 slot.

[Godlygamer23]

Most boards allow PCI gen selection. So you could just put the board in 2.0 mode so it's x8 on the bottom slot which should work fine then.

x8 refers to the number of lanes present. When PCIe slots are x4, x8, x16, etc., it's referring to the number of physical lanes in the slot. If slots are PCIe x16 physically but x4 electrically, there are 4 lanes present. You cannot go beyond it.

[Litargirio]

My 660 Ti runs on a PCIe 2.0 x4 slot.

 

I call hax.

[Godlygamer23]

I call hax.

Nope.

[AMICLG]

x8 refers to the number of lanes present. When PCIe slots are x4, x8, x16, etc., it's referring to the number of physical lanes in the slot. If slots are PCIe x16 physically but x4 electrically, there are 4 lanes present. You cannot go beyond it.

While yes on a board that only has a x4 slot electronically. But with a board that can be full x16 or x8 with the right CPU is a completely different story ie: LGA 2011 is what I was referencing. 

 

So a 5820K only has 28 PCI-E lanes. Meaning on a M-ATX board it'll run as x16/x8/x4 at 3.0. But if you go into the PCI-E setting you can set all 3 slots to be 2.0 thus it'll run at x16/x16/x16. And yes that x4 will change as it's electronically controlled which is why a CPU with 40 lanes like a 5930K will run at x16/x16/x8.

 

Also how do you think boards with a 4790K can do quad SLI. They have PLX controllers in them.

[Godlygamer23]

So a 5820K only has 28 PCI-E lanes. Meaning on a M-ATX board it'll run as x16/x8/x4 at 3.0. But if you go into the PCI-E setting you can set all 3 slots to be 2.0 thus it'll run at x16/x16/x16.

Can you show me a board where this occurs? You didn't mention any board.

[Litargirio]

Nope.

 

 

mind = blown