Understanding PCI Express 2.1 Stats and GPU Stats

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compa008

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Dec 13, 2011
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So first things first I have a few questions,

1.) PCI-Express 2.1 = 8GB/sec or 500MB/sec per bidirectional lane - Right?
2.) If I have a AMD 6970 I am using 176 GB/s memory bandwidth (maximum) per bidirectional lane - Right? If I'm crossfiring 2 6970s I'm using 352 GB/s memory bandwidth - Right?
3.) So in total I'm using 352 of 500GB/s for PCI Express 2.1 <u><b>OR </b></u>the fact that I have 2 PCI Express 16x slots I am using 352 of 1,000GB/s ? In other words the 500GB/s memory bandwidth (maximum) is just for one card?

6970 Specs:
http://www.amd.com/US/PRODUCTS/DESKTOP/GRAPHICS/AMD-RADEON-HD-6000/HD-6970/Pages/amd-radeon-hd-6970-overview.aspx#2
 
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You see, actually there is no card able to be bottleneck by 2.1 actually, maybe next year we gonna see the bottleneck, but for now anything gonna be fine on 2.1
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compa008

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Alright, I guess I'm getting confused.

So if I want to upgrade how do I know when my new graphics card is going to bottleneck the PCI Express 2.1 lane? Would a 7970 be under utilized with PCI 2.1?
http://www.amd.com/US/PRODUCTS/DESKTOP/GRAPHICS/7000/7970/Pages/radeon-7970.aspx#3

How about a R9 290:
http://www.amd.com/us/products/desktop/graphics/r9/pages/amd-radeon-hd-r9-series.aspx#5
 
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InvalidError

InvalidError

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There currently still aren't any games or GPUs that experience significant bottlenecking on a PCIe 2.x x16 slot.

If you use dual GPUs each running at 2.x x8 then there may be a 3-5% performance penalty compared to 3.0 x8.
 
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ben123a9

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You see, actually there is no card able to be bottleneck by 2.1 actually, maybe next year we gonna see the bottleneck, but for now anything gonna be fine on 2.1
 
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compa008

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Good to know. Is there GPU stat that people use to identify if the graphics card will require more PCIe bandwidth than what is provided? Other than PCIe 3.0 GPU plugged into a PCIe 2.1 motherboard?
 
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ben123a9

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Look, a PCIe 3.0 card only means it's compatible with, not that it takes advantage of it, I don't have any comparison, but I remember I saw a video from Linus on youtube (good youtuber who you can trust) and it literraly took none advantage, so we can't know yet when graphic cards will take advantage of it.
 
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