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Bandwidth saying 8x in second PCI

Last response: in Graphics & Displays
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March 12, 2012 5:07:06 PM

i7 860 w/ H60
DF 85 case
Asus p7p55d pro mobo
Radeon 6970

I just got myself a new case, but i have a H60 cooler and it blocks off the first pci slot, so im forced to put it in the second. I knew the second slot is supposed to switch to 8x in crossfire, but I was under the impression that since it says its a 16x slot, it would be. GPU Z is reading it as 8x. I did the test in GPUZ to see if it was running on 8x because it was idling, but it did not change. I couldnt find any info about it being only 8x. Can anyone help me with this plz? Also, if it is the case that has to stay at 8x, would i get a large drop in performance, or would it be barely noticeable? Thanks T.H.

More about : bandwidth pci

a c 253 U Graphics card
March 12, 2012 6:39:08 PM

It is baerly noticeable and most motherboards will default to x8 when the two slots are occupied. There is no truth to the rumor that it would be half of the performance instead in order to see the dirrerence you have to mearure it with software because you can't notice it by yourself. Unless the motherboard has the NF200 chip the second slot will always drop to x8 which if you did a comparison between a board running two x16 and one running two x8 you would only see about a 5% drop off in fps. Not enough to worry about and in the future when buying a motherboard look for one with the nf200 chip and you can get at least two slots running at x16.
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March 12, 2012 8:26:10 PM

dsnyder24 said:
i7 860 w/ H60
DF 85 case
Asus p7p55d pro mobo
Radeon 6970

I just got myself a new case, but i have a H60 cooler and it blocks off the first pci slot, so im forced to put it in the second. I knew the second slot is supposed to switch to 8x in crossfire, but I was under the impression that since it says its a 16x slot, it would be. GPU Z is reading it as 8x. I did the test in GPUZ to see if it was running on 8x because it was idling, but it did not change. I couldnt find any info about it being only 8x. Can anyone help me with this plz? Also, if it is the case that has to stay at 8x, would i get a large drop in performance, or would it be barely noticeable? Thanks T.H.


Asus board are quite funny when it comes to PCI lanes since they do not have a dedicated PCI controller (or whatever it's called).

Have you per chance got something else in the PCI lanes like a sound card? If so that PCI lane may be sharing bandwidth with PCIe16x 2 making it reduce the speed down to 8x.

Also there is usually an option in the bios to lower the speed of one of the PCI lanes, if this option is enabled it may be slowing down your pcie slot aswell

Edit: Looks like your board does not support 16x on the Grey port.... Shame as the old Asus boards like the a8n32-sli did.
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a c 216 U Graphics card
March 12, 2012 8:30:08 PM

It is possible that the card isn't fully seated and it's using fewer lanes as a result. I've seen this quite a lot in the past, where a not quite seated card, or dirty connectors would force an AMD GPU to use x8, x4, or x2.
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a b U Graphics card
March 12, 2012 8:41:26 PM

I wouldn't sweat it if you can't get it up to x16. Even a 6990 struggles to max out an x8 link. A 6970 will have literally no difference in performance between x8 and x16.
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a c 216 U Graphics card
March 12, 2012 8:43:17 PM

willard said:
I wouldn't sweat it if you can't get it up to x16. Even a 6990 struggles to max out an x8 link. A 6970 will have literally no difference in performance between x8 and x16.


That's not entirely true. x8 can make between 2-5% difference from tests shown.
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a b U Graphics card
March 12, 2012 8:48:49 PM

bystander said:
That's not entirely true. x8 can make between 2-5% difference from tests shown.

I was under the impression that was only in SLI/Crossfire setups with the highest end cards. I stand corrected.
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a b U Graphics card
March 12, 2012 9:33:33 PM

dsnyder24 said:
i7 860 w/ H60
DF 85 case
Asus p7p55d pro mobo
Radeon 6970

I just got myself a new case, but i have a H60 cooler and it blocks off the first pci slot, so im forced to put it in the second. I knew the second slot is supposed to switch to 8x in crossfire, but I was under the impression that since it says its a 16x slot, it would be. GPU Z is reading it as 8x. I did the test in GPUZ to see if it was running on 8x because it was idling, but it did not change. I couldnt find any info about it being only 8x. Can anyone help me with this plz? Also, if it is the case that has to stay at 8x, would i get a large drop in performance, or would it be barely noticeable? Thanks T.H.

Got the manual ? look at page 40



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a b U Graphics card
March 12, 2012 9:45:07 PM

dsnyder24 said:
i7 860 w/ H60
DF 85 case
Asus p7p55d pro mobo
Radeon 6970

I just got myself a new case, but i have a H60 cooler and it blocks off the first pci slot, so im forced to put it in the second. I knew the second slot is supposed to switch to 8x in crossfire, but I was under the impression that since it says its a 16x slot, it would be. GPU Z is reading it as 8x. I did the test in GPUZ to see if it was running on 8x because it was idling, but it did not change. I couldnt find any info about it being only 8x. Can anyone help me with this plz? Also, if it is the case that has to stay at 8x, would i get a large drop in performance, or would it be barely noticeable? Thanks T.H.


The 2nd PCIe x16 slot probably only has 8 electrical lanes and PCIe 1 has 16 electrical lanes. When you install 2 cards the CPU automatically assigns 8 lanes for each card. This is normal for P55, P67 and Z68.

Blue = x16
White = x8
Black = x4

Put the card in the black slot and it'll be at x4. Simply because the lanes are limited on the circuit...
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March 12, 2012 9:56:27 PM

RussK1 said:
The 2nd PCIe x16 slot probably only has 8 electrical lanes and PCIe 1 has 16 electrical lanes. When you install 2 cards the CPU automatically assigns 8 lanes for each card. This is normal for P55, P67 and Z68.

Blue = x16
White = x8
Black = x4

Put the card in the black slot and it'll be at x4. Simply because the lanes are limited on the circuit...


The board doesn't support 16x on the second slot =((
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a b U Graphics card
March 12, 2012 10:06:44 PM



I know what it says...

http://www.asus.com/Motherboards/Intel_Socket_1156/P7P5...

It's P55, thus limited by the PCIe controller on the CPU to 16 lanes. Board manufactures typically didn't electrically put 16 lanes on the 2nd PCIe slot as there was no reason too since the CPU was limited to 16 lanes plus to cut costs. So they wired (physically) 16 lanes to the 1st slot, 8 to the 2nd slot and 4 to the 3rd slot (which is controlled by the chipset).

Put 2 cards in the top 2 slots and the controller would assign 8 lanes to each and the chipset would shutoff the x4 PCIe slot (black)
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March 12, 2012 10:15:48 PM

2 x PCIe 2.0 x16 (single at x16 or dual at x8/x8 mode)
1 x PCI Express 2.0 x16 slots (at x4 mode, 2.5GT/s)
2 x PCI Express 2.0 x1 (2.5GT/s)
2 x PCI

It says it does, but probably will not. Mobos need the GPU cards to be in the first slot for x16. Say that this is the reason you bought the board and try to get a credit. Otherwise stick with the x8.

It is just stupid advertising to say 2x x16 slots, when it can only by the first slot.
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March 12, 2012 10:25:58 PM

I'm serious, who cares? x8 vs x16 bandwith isnt what you would think. There is 1.0001 or 1.00001 performance increase. Who cares!!?!?
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March 13, 2012 1:06:19 AM

Ok, well as long as i'm not losing too much performance i'm ok with it. I do think it is dumb that they can advertise it as a 16x when apparently it never reaches it.. even in crossfire.
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