PCI-e 1.1 x8 card in PCI-e 2.0 x8 slot running as x4???

[digityzed]

I'm interested in a dual port 10 Gbe SFP NIC that's PCI-e 1.1 x8. I have a PCI-e 2.0 x8 slot that's running as a x4 available on the motherboard. Will the NIC perform at full capacity (10 Gbps) or will it perform at half the rate (5 Gbps)??

 

[herrwizo]

[strike]It will work at full speed, since PCI-e 2.0 x4 provides exactly the same bandwidth as PCI-e 1.1 x8. Using the same analogy, you can guess that PCI-e 3.0 x2 is also the same in terms of bandwidth 😉[/strike]

EDIT: Ignore the post above, the card will work at x4, but by using PCI-e 1.1 protocol, so half speed.

 

[atomicWAR]

It will work at full speed, since PCI-e 2.0 x4 provides exactly the same bandwidth as PCI-e 1.1 x8. Using the same analogy, you can guess that PCI-e 3.0 x2 is also the same in terms of bandwidth 😉

Actually no i don't believe it will that is not how the backwards PCIe spec works. His card is 1.1 x8 which needs 2GBs to run full speed. His slot is PCIe 2.0 x8 but limited electrically to x4 (which is 2GBs under PCIe 2.0) so any card he plugs in regardless of PCIe spec will run at x4 speed with only 1GBs bandwidth in the case of PCIe 1.1.

 

[atomicWAR]

His PCIe is capable of the speed he needs in theory but when it defaults his card to x4 that speed he needs is lost.

 

[herrwizo]

Depends on the mobo design and the card itself, but it is indeed possible. What do manufacturer's specs of the card say? Did anyone use it with PCI-e 2.0 x4, any reviews?

 

[atomicWAR]

Sounds like the OP is in sketchy waters at best. If they don't mind it running at half speed I'd give it a go otherwise I might try to figure something else out like getting a different NIC.

 

[atomicWAR]

everything I am reading on the PCIe spec says a older PCIe version runs at the native PCIe link speed but at the slower protocol speed.

ie a PCIe 1.1 x8 card in a PCIe 2.0 x4 slot...runs at PCIe 1.1 x4. Unless you can find info otherwise and post it I'll stick with what wiki/SIG say when advising OPs. Would be happy to be wrong so part of hopes you post something new for me.

 

[herrwizo]

Nah, sounds correct, cannot find anything that claims otherwise. Peculiar situation, one that rarely occurs in practice.

The OP might indeed do the best by just getting a more modern NIC card.

 

[atomicWAR]

Nah, sounds correct, cannot find anything that claims otherwise. Peculiar situation, one that rarely occurs in practice.

The OP might indeed do the best by just getting a more modern NIC card.

Man you had my hopes up...lol. Well never hurts to wish.

 

[digityzed]

Ya, I searched and searched and couldn't find anyone with the same dilemma. It makes sense the PCI-e version would jump down as the card can't physically make a x8 slot functioning as a x4 slot run in x8 (heh... boy, that just sounds confusing). Why do mobos even have larger slots that function only with smaller lanes???