RIVBE XFire + PciE SSD drops second GPU from x16 to x8

[therealsummoner]

Hi again,

I have these with RIVBE (BIOS 0602):
4930k
2 x Sapphire 7970 GHz Ed. (x16 slot #1 + #3)
OCZ Revodrive 3 240GB (PciE x4) in the last x8 slot

GPU POST in BIOS shows the first GPU at x16 and the second as x8.
If i put the SSD into the first x1 slot then ofc it slows down, but both cards will be initialized as x16.

Now if i use the PciE Simulator in BIOS and set the last x8 slot to OCCUPIED, then again both cards are signaled as x16...

Basically a PciE x4 device in a x8 slot consumes somehow half of the second GPU's link speed.
Anyone has any clarification/explanation on this?


PS: I cannot test the middle x8 slot due to the huge cooler of the first GPU.

[philly_cheese_s]

therealsummoner wrote:
Hi again,

I have these with RIVBE (BIOS 0602):
4930k
2 x Sapphire 7970 GHz Ed. (x16 slot #1 + #3)
OCZ Revodrive 3 240GB (PciE x4) in the last x8 slot

GPU POST in BIOS shows the first GPU at x16 and the second as x8.
If i put the SSD into the first x1 slot then ofc it slows down, but both cards will be initialized as x16.

Now if i use the PciE Simulator in BIOS and set the last x8 slot to OCCUPIED, then again both cards are signaled as x16...

Basically a PciE x4 device in a x8 slot consumes somehow half of the second GPU's link speed.
Anyone has any clarification/explanation on this?


PS: I cannot test the middle x8 slot due to the huge cooler of the first GPU.

I couldn't find the RIVEBE manual, I assume they r the same? Anyway found you this, pretty much explains what happens when each lane is occupied.


Funny part is mine only runs my GPU'S at PCI-E 2 not PCI-E 3, how ever there is a FORCE PCI-E 3 out there....

[therealsummoner]

Yep it is something similar, but then this means if i'd pop the SSD into slot 2 (between the two GPUs), it would "set itself up" as shown at the Trifire part in the table? I.e. x16/x8/x16 (while of course the SSD will only set the slot to x4)?

And then, with the SSD in the last slot "forces" the second GPU to go x8 instead of x16?
Maybe this would mean if there is anything in the last x8 slot, the second GPU will just drop to x8? Then the PciE Simulator is not correct on this.

[therealsummoner]

Well here is the deal:
My water cooling is half complete (only the two graphics cards atm) thus i was able to sit the Revodrive between the two x16 slots into the x8 slot and everything is good, i.e. both cards are @x16.
The only craziness is similar to what philly cheese steak told above - the second card went down to PciE GEN2 only. The first card stood at GEN3.
I was hoping the second card can go back to GEN3 with forcing the Revodrive's slot down to GEN2 only in the BIOS (Revodrive is GEN2 btw), but no go.
Anyway, i'm ok now with all these, since benchmarks show zero difference between GEN2 and 3.

Just letting people know about my experiments. 😉