XF/SLI/Physx 2nd GPU on PCIE 1.0 x4 width (x16 physical) on P35 -- what GPUs work well; extreme bottleneck?

[QuixoticOne]

I've got a P5K-E type motherboard that supports a primary x16 actual slot and a secondary x4 wide (x16 physical) slot.

I'm considering the possible use of either a pair of 8800GTs or pair of 4850s on this board for multi-monitor usage, possibly a physx processor use (using a 2nd 8xxx GPU in this x4 slot), and of course I'd be in theory able to use the 4850s in Crossfire X if I wanted.

I'm wondering if the boards (8800GT or 4850) will even WORK in the x4 width slot though since IIRC I've never been able to boot successfully and get video out of an 8800GT in the 2nd (x4) slot even though the PSU and power situation is fine. I'm not even talking about SLI, I just mean as an independent card it seemed not to work for some unknown reason even though an 8600 will work in that x4 slot according to past experience.

Is the 8800GT supposed to work in an x4 wide slot (even not using SLI)?

Does an 4850 work at all in an x4 wide slot? If so would it work well as part of a CF-X pair given that the other 4850 would be in an x16 slot?

What about using a 2nd 8800GT or 8600GT as a PHYSx board in the x4 slot? Would that work well or would the x4 be too much of a bottleneck even for that use?


Thanks in advance!

 

[mpilchfamily]

So i guess you have open ended slots. Otherwise you wouldn't be able to plug an 8800 into a 4x slot. But you seam to already have your answer. No an 8800 will not work in a 4x slot. It requires more bandwidth then the 4x offers. The 8600 will work since it can get by with only the 4x's available bandwidth. If you place a card in the 4x slot it will just be another video card for use with multiple monitors. It will not act as a physics porc. Support for a 3rd GPU to run as a Physics proc was the idea with the boards that support tri SLI and tri CF but was virtually abandoned. The new card take one most of the physic possessing already so there is no need for an independent card to do such task.

CF and SLI at set only to run on the available 16X slots on the board. You can not force it over to work on the other PCI-e slots. All the other PCI-e slots are for other cards. But you can also plug any other sized PCI-e card into the second 16x slot without a problem.

 

[QuixoticOne]

Thanks for the reply.

Well it has two full sized (physically) x16 slots, but one of them is limited to x4.

As for the 8800GT not working in x4, I thought maybe it was just a bad BIOS or driver or some such issue and that with the right BIOS and right driver (e.g. Windows) it might work. I'd only ever tried it in LINUX. So I thought maybe it'd work better with a different / new driver.

I've never tried a pair of 4850s in a P35 P5K-E/Deluxe type M/B with one of the slots being x4, so I really had no idea if it'd work or not; supposedly this is a crossfire compatible motherboard, though, but I assume that doesn't help the 2nd GPU exceed its x4 PCIE slot bandwidth so even if it worked there'd be some question of bottleneck. IIRC there was some article showing GPUs performing much better in benchmarks with dual x16/x16 slots as opposed to an x16/x8 slot pairing, but I forget the details as to how bad it really was, and I don't know how applicable that'd be to the 4850 with current drivers anyway since I hear they keep making improvements in XF scaling and such...

I have heard that people get some useful PHYSX benefits (in the 3-4 games that even support it) from having even a lowly 8600 2nd GPU installed, so I thought it'd be a possibly good additional benefit of using another 8800GT if that could work in the x4 slot which apparently it won't. Seems like NVIDIA kind of shot themselves in the foot not letting the 8800s work in x4 slots or SLI on non-SLI motherboards yet also touting the benefits of a 2nd GPU for either SLI / hybrid SLI / PHYSX when the fact appears to be that nobody with most P35s could possibly even take advantage of that given the 2nd x4 slot and non-SLI M/B.

 

[apoppin]

they work .. even an 4870x2 "works" in the 4x PCIe slot, physically; - my 4870/512 ran in Crossfire X3 in my Gigabyte P35's 2nd 4x slot with my 4870x2 in the 16x slot

However, there was not much improvement in the overall performance - largely due to drivers; but the 4x slot *kills* the 2nd card's performance

i am testing this - right now! .. after, i am changing out my MB to x48 Asus P5e as soon as i format and do a fresh Vista install [again]

Now i DID run 2900xt crossfire with a 2900xt in the 16x slot and my OC'd 2900p in the 4x slot; there was very decent improvement when CF scaled. But then the 2900xt is half as fast as the 4870

 

[QuixoticOne]

Thanks for the 4870 in an x4 slot info. I'm glad the card works in such a slot anyway, but that's too bad that it hurts the performance so much. Is there any XF mode/option tuning that you can do to get it to take the maximum advantage of the combination of the high performance slot/card being coupled with the low performance slot/card?

 

[SunnyD]

PCIe autonegotiates the appropriate channel width provided the amount of requested channels are electrically available in the socket. Hence you can put a 16x card in a 1x socket (assuming either an open ended socket or a 16x physical socket with 1x electrical connection). Thus is the nature of PCIe... the only difference is the amount of available bandwidth to the card.