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Will a 4870x2 be bottlenecked by x8 PCI-E slot

Last response: in Graphics & Displays
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August 22, 2009 10:03:48 AM

Title sums it up, will a 4870x2 be bottlenecked by x8 PCI-E slot? Im looking into a future build, I would be running a Phenom 2 955 BE
August 22, 2009 1:09:57 PM

^ well x8 2.0 will bottleneck even a 4850 from (iirc) anandtech's results.
Related resources
August 22, 2009 8:13:37 PM

Quote:
Again, links.

+1, I wanna see real results please. I can't decide on what motherboard to get, and this is a defining factor of which one I chose.
August 22, 2009 8:25:04 PM

LegionHardware did a comparaison long time ago, 4850 was slightly bottlenecked by pcie 8x 2.0
http://www.legionhardware.com/document.php?id=761&p=2

P.S: They were comparing crossfire 4850's in multiple configuration (pcie 16x 2.0, pcie 8x 1.0, yadayada) against a single 4850. And when they put the configuration in pcie 16x 2.0, they had more gain than the pcie 8x 2.0.
August 22, 2009 9:55:09 PM

Quote:

That legion hardware test has nothing to do with the subject, why post it. There are too many variable's and correct me if I am wrong but it does not give any analysis to bandwidth usage nor does it aim to.


Unless I really did not understand the question or the article, I think it has to do with the subject: This is how I see it:
Only compare the x38 and the P45 results, they use the same pieces except for the motherboard.
When we look at the Crysis test (a GPU intensive game) they got a 41.3% improvement in fps over a single 4850. Now when they use a board that uses 8x lanes, they only get 37.1 %. Only the motherboard changed and the FPS advantage a x48 gives you a p45 isn't that much. That is why I think it is safe to presume that the 4850 is on the edge of pcie 8x limit. And a 4870x2 is way more powerfull, so it will defenitly be bottlenecked.

I agree it isn't perfect, but eh.
August 22, 2009 10:15:59 PM

I have a GTX 295 with a PCI-E 1.1 and I can say that there is no bottlenecked.
August 22, 2009 10:28:43 PM

BigBurn said:
LegionHardware did a comparaison long time ago, 4850 was slightly bottlenecked by pcie 8x 2.0
http://www.legionhardware.com/document.php?id=761&p=2

P.S: They were comparing crossfire 4850's in multiple configuration (pcie 16x 2.0, pcie 8x 1.0, yadayada) against a single 4850. And when they put the configuration in pcie 16x 2.0, they had more gain than the pcie 8x 2.0.

For high end SLI and Crossfire, PCI-E 8x 2.0 can certainly be a disadvantage, but that's because the two cards must constantly share information over the system's PCI-E bus.

A dual GPU card has it's own internal connections. PCI-E 8x 2.0 should only make a very small difference (or no difference at all) with any single slot setup, even a GTX 295/ 4870x2.

Point is, SLI/Crossfire vs. single slot is a night and day difference as far as PCI-E bandwidth is concerned.
August 22, 2009 10:37:07 PM

Quote:
For high end SLI and Crossfire, PCI-E 8x 2.0 can certainly be a disadvantage, but that's because the two cards must constantly share information over the system's PCI-E bus.

Oh, didn't knew that(well I knew they needed to sahre stuff, jsut didn't think it would make that much of a difference...). I guess we still learn everyday XD.

BUT, OP said "Im looking into a future build". So maybe he is talking about the (somewhat) new am3 motherboard that runs at 8x when doing crossfire. But then, if he only use one card, even if it's a X2, the lane will run at 16X right?



August 22, 2009 11:50:13 PM

Alot has to do with the chipset as well.
These links wont give diffinative data, but does help understanding about the process, and its limitations.
At least data as pertains to the main question here
August 23, 2009 9:44:44 PM

I think the better question would be why is a 4870x2 going in an x8 slot?

If it's for CF quad, then the point is basically moot - you should be prepared to hit bottlenecks left and right in a quad GFX setup...

If it's for an old mobo (were there ever any mobos that had an x8 PCIe 2.0 slot only?) it's likely PCIe 1.0 x8, which means it'll be a fairly significant bottleneck. However, since it's such an old system, I would imagine your CPU would be the bottleneck there, not the bus between them.

If it's for a dual monitor/dual gfx card setup, then the point is moot again. There is no way that the bus is going to be the bottleneck even if you have 2x 30" monitors hooked up running a separate game (or openGL app) in each. The drivers are likely going to stop you from doing that at any decent speed, and even if they didnt, the CPU or ram would likely be the bottle neck.

So I have to ask - why is this question being asked :S
August 23, 2009 9:51:55 PM

It never occurred to me the other card could be something other than a GFX card >.<

I fail.

I know he mentioned the PHII 955, but it was just a situation that a dual gpu card could end up in an x8 slot

edit: toms did tests about the bottlenecks of PCIe 1.0 years ago, and the 8800s in SLi were able to hit a bottleneck under x8... I'm assuming newer cards would use the same or more bandwidth (more bandwidth because of newer games, not because of more powerful cards)

They did a test recently too under triple SLi with x58 boards... I'll look for the link and edit it in, but basically with triple sli they hit a massive bottleneck at x4, and a slight bottleneck at x8

edit 2: http://www.tomshardware.com/reviews/crossfire-pci-expre...

This is even better than the ones I was talking about, this is -single gpu- bus performance. At high gfx settings, it's clear that the x16 1.0 had a disadvantage to the x16 2.0.
August 23, 2009 10:16:21 PM

And all skt 1156 is limited to 8xPci-2
And the new cards will have x2 iterations as well
I say were close to reaching those limitations, and Intel is being sneaky limiting their skt 1156, mandating a 2 tier class
August 23, 2009 10:18:24 PM

The cpus run on 1156 will have as much poential as the 1366 cpus, but wont be able to fully utilise a cf/sli solution
!