Tom's Hardware > Forum > Graphic & Displays > ATI > 4870 will bottleneck in pci-e x16 1.0?

4870 will bottleneck in pci-e x16 1.0?

Forum Graphic & Displays : ATI - 4870 will bottleneck in pci-e x16 1.0?

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Greg86   06-27-2008 at 05:51:00 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?

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jamesgoddard   06-27-2008 at 05:54:24 PM
- -1 +

Yeah - the PCI-e x16 1.0 will seriously bottleneck the card - you may loose a whole 0.1% in performance

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copasetic   06-27-2008 at 06:11:29 PM
- 0 +

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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modtech   06-27-2008 at 06:33:27 PM
- 0 +

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

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jevon   06-27-2008 at 06:54:11 PM
- 1 +

http://www.tweaktown.com/articles/ [...] index.html

PCI-E 2.0 x8 is essentially a 1.1 x16 electrical lane as 2.0 has doubled bandwidth. If I understand that correctly at least!

But yeah, I would want a 2.0 x16 lane per 4870!

Reply to jevon
david714   06-27-2008 at 06:58:05 PM
- 0 +

It won't bottleneck. PCI-E 2.0 is not twice the speed of 1.1, there are just some optimizations to the protocol.

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copasetic   06-27-2008 at 06:59:23 PM
- 0 +

modtech wrote :

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/review [...] 15-10.html

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.

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ravynmagi   06-28-2008 at 12:21:29 AM
- 0 +

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.

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dagger   06-28-2008 at 12:30:33 AM
- 0 +

ravynmagi wrote :

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/ [...] index.html

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ravynmagi   06-28-2008 at 02:21:19 AM
- 0 +

But I'm having some doubts about the Tweaktown article. Was hoping to at least see another test like it to confirm the results.

------------------------------ ▪ Core 2 E6750 @ 3.6GHz ▪ Abit IP35 Pro rev 1.1
▪ Buffalo Firestix 4GB DDR2-900 ▪ EVGA 8800 Ultra
▪ WD Raptor 74GB - (3) Seagate 7200.10 400GB
▪ Seasonic M12 700 ▪ CM Cosmos
 Reply to ravynmagi
jaydeejohn   06-28-2008 at 02:42:21 AM
- 0 +

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

------------------------------ I went drifting, thru the capitols of tin, where men cant walk and cant freely talk, and sons turn their fathers in
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