PCI Express 3 card on PCI Express 1 motherboard

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PCI Express 3 card on PCI Express 1 motherboard

Postposted on Tue Feb 11, 2014 7:37 pm

My current motherboard only has PCI Express 1. I understand that PCI Express is backward compatible, so a current PCI Express 3 card could be installed. If I do so, would I lose all of the benefit of upgrading the video card, or most, or very little?
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Re: PCI Express 3 card on PCI Express 1 motherboard

Postposted on Tue Feb 11, 2014 7:43 pm

1. It should work, but the card will fall back into PCIe 1.0 mode.
2. If the slot is x16 both physically and electrically (meaning the slot is the same physical length as the connector on the card AND there are actually electrical connections to the PCIe hub for all 16 lanes), then PCIe 1.0 won't hurt game performance by a huge amount.

3. BUT: If you only have PCIe 1.0, then you are likely dealing with a very old system [the 5 year old Core 2 I replaced last year was already on PCIe 2.0], so adding in a new high-end video card may end up bottlenecking on a slower component like the CPU. A low to mid-range modern GPU (roughly $150 max price) should give you a noticeable boost in 3D games, but don't expect miracles on an old machine.
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Re: PCI Express 3 card on PCI Express 1 motherboard

Postposted on Tue Feb 11, 2014 7:56 pm

chuckula wrote:2. If the slot is x16 both physically and electrically (meaning the slot is the same physical length as the connector on the card AND there are actually electrical connections to the PCIe hub for all 16 lanes), then PCIe 1.0 won't hurt game performance by a huge amount.

Does this answer the question? "x16 running at x16".

chuckula wrote:3. BUT: If you only have PCIe 1.0, then you are likely dealing with a very old system [the 5 year old Core 2 I replaced last year was already on PCIe 2.0], so adding in a new high-end video card may end up bottlenecking on a slower component like the CPU. A low to mid-range modern GPU (roughly $150 max price) should give you a noticeable boost in 3D games, but don't expect miracles on an old machine.

August 2009, so 4½ years old. I realize there's a limit to upgrading part by part.
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Re: PCI Express 3 card on PCI Express 1 motherboard

Postposted on Tue Feb 11, 2014 8:02 pm

Well....if we take your question at face value and only discuss the PCIe interface as a limitation, then it depends on how powerful a card you would be using. A high-end card like a 780 or 290X might see a significant performance penalty with PCIe 1.0, whereas an entry-level $50 card might not be affected at all (because it's too slow to exceed the bandwidth in the first place).


As chuckula mentioned, PCIe 2.0 boards have been out for quite some time (2007-08), so I think the bigger problem would be an old system with a slow CPU.
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Re: PCI Express 3 card on PCI Express 1 motherboard

Postposted on Tue Feb 11, 2014 8:06 pm

Yan wrote:Does this answer the question? "x16 running at x16".



Yes, x16 running at x16 is exactly what you want. As long as you are realistic about your performance expectations, then a GPU upgrade should give you positive results in games, and don't worry about the PCIe part of the equation.
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Re: PCI Express 3 card on PCI Express 1 motherboard

Postposted on Thu Feb 13, 2014 10:23 pm

I ended up replacing my HD 4870 with an R7 250. I was surprised about how small it was, and that I didn't have to plug a molex into it. I guess I'm 5 years out of date. Image

I had done some synthetic benchmarks on my HD 4870, and was very surprised that the R7 250 had essentially the same results. Passmark even specifically says that a HD 4870 has a rating of 1360, while an R7 250 has an almost identical rating of 1376. On the other hand, I could see that the tests were running noticeably faster and better, and a short try with Crysis 2 convinced me that the graphics performance was indeed much better. Are these synthetic tests really that useless? Or is what they measure actually unrelated to the video quality I observe?

3D Mark told me that my new card was the same as a HD 8670. Oh, and it can mine Litecoins at 146 kH/s. I don't think I'll be doing a lot of that, though. Image
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Re: PCI Express 3 card on PCI Express 1 motherboard

Postposted on Thu Feb 13, 2014 11:48 pm

It's difficult to find benchmark results over multiple generations of cards but I'm not sure an R7 250 would be noticeably faster than a 4870.

If you could afford a 260x you would see a much bigger jump in performance.
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Re: PCI Express 3 card on PCI Express 1 motherboard

Postposted on Fri Feb 14, 2014 1:30 am

Makes next to no difference, even with the highest-end GPUs.

http://www.pugetsystems.com/labs/articl ... 80pResults
PCIe 1.1 x16 = PCIe 2.0 x8, and as you can see there is little to no difference even compared to PCIe 3.0 x16

Image

More tests, including Titan SLI @ 4k in the link.
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Re: PCI Express 3 card on PCI Express 1 motherboard

Postposted on Fri Feb 14, 2014 12:03 pm

jihadjoe wrote:Makes next to no difference, even with the highest-end GPUs.
http://www.pugetsystems.com/labs/articl ... 80pResults
PCIe 1.1 x16 = PCIe 2.0 x8, and as you can see there is little to no difference even compared to PCIe 3.0 x16
More tests, including Titan SLI @ 4k in the link.

I find it hard to believe that there was no impact whatsoever on the PCIe 2.0 x8 (same as 1.0 x16). I wasn't expecting a huge impact, but I seem to remember Anandtech doing some tests where they saw at least measurable differences. I wonder if the motherboard those guys were using wasn't actually dropping down to PCIe 2.0.

Either way, the card he ended up choosing isn't fast enough to matter.
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Re: PCI Express 3 card on PCI Express 1 motherboard

Postposted on Fri Feb 14, 2014 12:54 pm

^
Maybe under crossfire it does. AMD did admit that their crossfire connector lacks the necessary bandwidth so they have to transfer data through the PCIe bus.
Nvidia, on the other hand seems to have things well in hand with their SLI bridge and thus isn't negatively affected.

Found the AT articles you meant.

Higher link speeds does show some scaling on the 7970, but in almost all cases PCIe 3.0 x4 (equal to PCIe 1.1 x16) seems sufficient.
Image

It's only when things drop down to 3.0 x2 (basically PCIe 1.1 x8) that things get nasty.
Image

AT's Nvidia Titan results show no difference at all for single monitor, much the same as the pugetsystem's tests above:
Image

But does show a tiny bit of scaling with multi-monitor. Possibly something to do with frame buffers being copied around for each screen?
Image


.: PCIe 1.1 x16 is more than sufficient.

I also recall reading another article that shows the link speed matters less when frame rate is bound by the render-side of the GPU. Can't find that link at the moment but I'll update this post if I do.


Yan wrote:Are these synthetic tests really that useless? Or is what they measure actually unrelated to the video quality I observe?


From passmark themselves: http://www.videocardbenchmark.net/graph_notes.html :wink:
Real Life Performance Comparison
The rating the Video Card’s are given here represents their peak performance for the type of load generated by the tests and will not necessarily match the real world performance with any specific software application or game.
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