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4870 will bottleneck in pci-e x16 1.0?

Last response: in Graphics & Displays
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June 27, 2008 3:51:00 PM

Hey yall,

I've read on some other forums that due to the new GDDR5 memory that's in these cards, its highly recommended to run them in pci-e 2.0 because they really need the bandwidth, and that running them in pci-e x16 1.0 will significantly bottleneck their performance. Anyone know anything about this?
June 27, 2008 3:54:24 PM

Yeah - the PCI-e x16 1.0 will seriously bottleneck the card - you may loose a whole 0.1% in performance
June 27, 2008 4:11:29 PM

The CPU will bottleneck it long before the PCI-E bus does. The 9800 GX2 doesn't start bottlenecking until PCI-E 2.0 x4, which has the same bandwidth as x8 on PCI-E 1.0. I haven't seen a review for the 4870 yet that tests this, but I don't expect at x16 it'll make any difference.

4GB/s of bandwidth is a lot to fill.
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June 27, 2008 4:33:27 PM

Is that tested with lots of AF/AA @ high res because that would require a lot more bandwidth than regular settings at regular res.
June 27, 2008 4:58:05 PM

It won't bottleneck. PCI-E 2.0 is not twice the speed of 1.1, there are just some optimizations to the protocol.
June 27, 2008 4:59:23 PM

modtech said:
Is that tested with lots of AF/AA @ high res because that would require a lot more bandwidth than regular settings at regular res.

Here's a link to the review I'm talking about

http://www.tomshardware.com/reviews/pci-express-2-0,191...

Flight Simulator X is the only game that gets hit more than 1% or so at 2.0 x8.

AA and AF shouldn't have too much of an impact, since the textures being sampled are stored in the GPU memory. They don't need to travel through the PCI-E bus that often, relatively speaking.
June 27, 2008 10:21:29 PM

I thought PCI-E 2.0 is twice the bandwidth. I've ready PCI-E 1.1 is 250MB/s per lane and PCI-E 2.0 is 500MB/s.

I would of never imagined the 4870 would bottle next PCI-E 1.1 16 lanes or PCI-E 2.0 8 lanes, but one review claims it does very slightly. Still not sure.

However this talk has me really concerned about the 4870 X2 I'm planning to get with my P35 board. If the 4870 is even slightly bottlenecked, then I might have to upgrade to a PCI-E 2.0 motherboard before getting the X2.

I was kinda hoping to hold on to my P35 board until the X58 came out late this year.
June 27, 2008 10:30:33 PM

ravynmagi said:
I thought PCI-E 2.0 is twice the bandwidth. I've ready PCI-E 1.1 is 250MB/s per lane and PCI-E 2.0 is 500MB/s.

I would of never imagined the 4870 would bottle next PCI-E 1.1 16 lanes or PCI-E 2.0 8 lanes, but one review claims it does very slightly. Still not sure.

However this talk has me really concerned about the 4870 X2 I'm planning to get with my P35 board. If the 4870 is even slightly bottlenecked, then I might have to upgrade to a PCI-E 2.0 motherboard before getting the X2.

I was kinda hoping to hold on to my P35 board until the X58 came out late this year.

It's more than just "slightly" bottlenecked. And yes, pcie2.0 is twice the bandwidth.
http://www.tweaktown.com/articles/1472/7/page_7_benchma...
June 28, 2008 12:21:19 AM

But I'm having some doubts about the Tweaktown article. Was hoping to at least see another test like it to confirm the results.
June 28, 2008 12:42:21 AM

I think using a 16x is fine at this point, but looking at these boards that use only 8x or less is when youll see a dropoff. Thats for xfire. If yyoure currently running 16x youre ok, no matter the config
March 3, 2010 8:37:01 PM

David714 is wrong...
PCIe 2.0 is 500 MB/s per lane
PCIe 1.0 is 250 MB/s per lane
!