PCI-E 16x slot only running as 8x? Gigabyte P67A-UD5-B3

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cold_steel

Gawd
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Jun 27, 2004
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Hey guys,

Specs: Gigabyte P67A-UD5-B3, 2600K @ 4.2GHz, 8 GB PC3 1600


I've been using an EVGA GTX570 for quite some time and I just stepped up to the Galaxy GTX780 HOF card. After I got the new card in I downloaded GPU-Z to check out the new shiny specs, and I noticed it is only running at 8X when this board supports 16X. I tried stressing the card with the GPU-Z load option and also with rthdribl but it stays at 8X.

I hadn't looked at anything with GPU-Z in ages, so I popped my GTX570 back in- its also reporting 8X.

The only other PCI-E device I'm using is an ASUS Xonar Xense in the bottom 4X slot, which shouldn't be sharing with the 16X slot. I did try removing it and testing again, still 8X.

I did just flash my BIOS to the latest version just before doing all of this, and I did not look to see what the link speed was before doing that. I've looked all over the BIOS and I don't see any kind of speed setting.

Please spare me the "8X isn't saturated" comments, I'm aware. I'm just trying to figure out why this 16x slot is not running 16x. Is it possible I'm getting ratty data from GPU-Z and CPU-Z? Or am I missing a setting somewhere?
 
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Do you have the other PCIE slots populated? I think the p67 could only handle 1x16 configuration. If you are using more then one slot it will bump down to x8

If that is not true then reseat the card and also check for dust in the slot. I had a dust bunny once that knocked my card down to x8.
 
cold_steel said:
The only other PCI-E device I'm using is an ASUS Xonar Xense in the bottom 4X slot, which shouldn't be sharing with the 16X slot. I did try removing it and testing again, still 8X.
Click to expand...

Dusting is a good idea though. let me break out an air can and give that a shot. I'll report back.
 
PCI-e 3.0 8x is the same speed as PCI-e 2.0 16x

I think you card is running in PCI-e 3.0 mode.
 
Spazturtle said:
PCI-e 3.0 8x is the same speed as PCI-e 2.0 16x

I think you card is running in PCI-e 3.0 mode.
Click to expand...

That board does not support PCI-e 3.0

And the above poster is correct, populating ANY 2 PCI-E slots defaults to 2x 8 lanes.

Its a 2+ year old chipset and board, running a brand new card. Technology has changed :)

The good news is, it should not matter performance wise by more than a few percentage points.
 
jmilcher said:
That board does not support PCI-e 3.0

And the above poster is correct, populating ANY 2 PCI-E slots defaults to 2x 8 lanes.

Its a 2+ year old chipset and board, running a brand new card. Technology has changed :)

The good news is, it should not matter performance wise by more than a few percentage points.
Click to expand...

Gigabyte say it supports PCI-e 3.0

http://www.gigabyte.com/products/product-page.aspx?pid=3762#ov

also:

  1. 1 x PCI Express x16 slot, running at x16 (PCIEX16)
    * For optimum performance, if only one PCI Express graphics card is to be installed, be sure to install it in the PCIEX16 slot.
  2. 1 x PCI Express x16 slot, running at x8 (PCIEX8)
    * The PCIEX8 slot shares bandwidth with the PCIEX16 slot. When the PCIEX8 slot is populated with a PCI Express graphics card, the PCIEX16 slot will operate at up to x8 mode.
  3. 1 x PCI Express x16 slot, running at x4 (PCIEX4)
    * The PCIEX4 slot shares bandwidth with the PCIEX1_1 and PCIEX1_2 slots. When the PCIEX1_1 slot or the PCIEX1_2 slot is populated with an expansion card, the PCIEX4 slot will operate at up to x1 mode.
  4. 2 x PCI Express x1 slots
    (All PCI Express slots conform to PCI Express 2.0 standard.)
  5. 2 x PCI slots

So if he has the GPU in the top x16 slot and the Audio card in the x4 slot then he should be fine.

Its only if you use the x8 slot then does the x16 slot become x16
 
Dusting didn't help.

As stated previously, I did try removing the sound card and things didn't change, even though the 4x slot should not be sharing anything with the 16x.

Also this is not just happening on the new GTX780. It also happens on the GTX570, which is not new.

And even if this board supported PCI-E 3.0, my sandy bridge processor does not :)
 
So I figured out the issue!

Out of the blue as I was driving home, I happened to remember reading somewhere a long time ago that enabling USB 3.0 Turbo on these P67 boards would take lanes away from the 16X slot. I checked this when I got home, and it was enabled. After disabling this setting, both the GTX570 and the new GTX780 are running full PCI-E 2.0 16X (Sandy bridge CPUs can't do PCI-E 3.0)

This is with the ASUS Xonar Xense still in the 4X slot too :)

Thanks for the replies/ideas. Hopefully this will help someone else out!!
 
Is this something specific to those P67 boards?

Anyways, congrats on fixing the problem.
 
Spazturtle said:
Gigabyte say it supports PCI-e 3.0
Click to expand...

The processor needs to support it as well.
I believe the P67 series boards that support PCI-e 3.0 can only use x8, they were designed too early to test fully.
So you get the latency improvements from the faster switching speed but not the double bandwidth.
 
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