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me

join:2002-12-08
Iapetus
reply to Extide

Re: Using only the second PCIE x16 same speed ? for video card

The video card manual only talks about installing in a x16 primary slot. There is no mention of x8

Please provide a link that say x8 is enough for max performance.

»www.power-color.com/Manual/09010···_ENG.pdf
»www.amd.com/us/products/desktop/···w.aspx#3

JoelC707
Premium
join:2002-07-09
Lanett, AL
kudos:5

Ask and ye shall receive.

»Is pcie 3.0 really worth it?
»www.tomshardware.com/reviews/amd···8-5.html

It's not so much a direct comparison of x16 and x8 because you need to know the PCIe revision. 1.1 had a maximum bandwidth of 250MB/s per lane, 2.0 doubled that to 500MB/s per lane and 3.0 doubles that again to 1GB/s per lane. Thus we have the following:
PCIe 1.1 x16 - 4GB/s
PCIe 1.1 x8 - 2GB/s
PCIe 2.0 x16 - 8GB/s
PCIe 2.0 x8 - 4GB/s
PCIe 3.0 x16 - 16GB/s
PCIe 3.0 x8 - 8GB/s

PCIe bandwidth really comes into play for GPU computing or 3-way and 4-way video card setups. With just 1 or 2 video cards, you won't notice a difference.



me

join:2002-12-08
Iapetus

I used PerformanceTest 7.0 to test this out.

With a PCIE x1 card installed in second port (main port at x8)
-The graphics scores were only off by -1.6% for 2D and -1.2% for 3D

Strange thing is that cpu performance was lower by 9.2% at x8 compare to x16.

For the x8 test I had the case on its side and open (for easy removal of the card)
For x16 test I closed the case and stood it upright. Maybe heat had an effect.


JoelC707
Premium
join:2002-07-09
Lanett, AL
kudos:5

Interesting. The percentage differences on the graphics scores are probably within the acceptable margin of error for the test. Basically further proving x8 is all you really need except in specialty setups. What is intriguing is the CPU difference. That's a noticeable difference. I can't think of any reason why PCIe config of ANY kind would make such a difference.

It's possible heat played a role in the test as you undoubtedly had airflow differences but I can't imagine it got hot enough that quick to make that drastic of a change. If heat did cause that kind of a difference in what I would assume to be a relatively short test (long enough to swap the video card around, test it and swap back?), I'd say you might want to look at your cooling setup and see if there are any problems (dust filled heatsink or fan perhaps?).



me

join:2002-12-08
Iapetus


Two fans
I didn't move the video card. It stayed in primary slot. I stepped it down to x8 by adding a PCIE xl card in the secondary x16 slot.
Removing the extra card bumped it back to x16.

I'm using a good heat sink (Hyper 212) with two 90mm push/pull fans. Temps usually stay constant and low at around 35 degrees

JoelC707
Premium
join:2002-07-09
Lanett, AL
kudos:5

Ahhhh OK, makes sense. And excellent choice on the fan, it's probably the best choice for an air cooler. Still doesn't explain the CPU differences. I wonder if it's repeatable?



me

join:2002-12-08
Iapetus

A second test of the x16 mode resulted in only 4.5 CPU score difference.