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Crossfire question

Last response: in Graphics & Displays
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August 13, 2012 1:29:16 AM

Hello,

I have 2 x 6950 setup in crossfire, card one says bus interface is :p CI-E 2.0X16 @16 2.0

The second is : bus interface PCI-E 2.0X16 @X4 1.1

My question is why the second card is not at the same PCI-E values?

Thanks

More about : crossfire question

August 13, 2012 1:59:47 AM

There are only a limited number of PCIe lanes available.

The exact configuration depends on the CPU and chipset that you have.

Sandybridge has 16 2.0 lanes which are connected directly to the CPU. Ivybridge has 16 3.0 lanes.

Sandybridge-E has 40 3.0 lanes.

There are also additional PCIe lanes available directly from the add-in chipset, usually an additional 6 or 8.

I am not sure how AMD has their PCIe lanes configured but as far as I know they're still on the chipset.

PCIe devices can have their link speeds configured in groups of 1, 4, 8, or 16. This is indicated by a certain pin on the connector itself. This means that a 1x or 4x card can be put into a 16x slot and it will work flawlessly. Similarly, a 16x card can have a good chunk of its PCIe connector sawed off and it will still work in a 1x or 4x slot. Similarly, a 16x card can have part of the connector covered in scotch tape and it will run at 1x, 4x, or 8x speed in a 16x slot.

Since 2 and 3 way graphics setups would ideally require 32 or 48 PCIe lanes they would collectively require more than are made available from the CPU and/or chipset. This necessitates that some or all of the slots have their link width reduced from 16x to 8x or 4x in order to allow the other cards to function. If one graphics card is used on a Sandybridge/Ivybridge processor it will run at 16x link width. If two graphics cards are used on a Sandybridge processor they will both run at 8x speed. If three are used they will run at 8x/4x/4x.

Since AMD chipsets do not yet have PCIe integrated into the CPU directly all PCIe lanes are provided directly from the chipset. On older Intel chispets and NVidia chipsets the same is true. High speed 2.0 lanes are made available from the northbridge while 1.1 speed lanes are made available from the southbridge. This means that in some 2/3 way setups one card may be running at 1.1 speed while the rest are running at 2.0. This was certainly the case with the NVidia 700 series chipsets.

If you can tell me what your motherboard model is I can tell you for certain what you should be expecting.
August 13, 2012 2:04:42 AM

Thank you very much for a good reply, my motherboard and specs are below:






Is there a way for me to have both cards running @16
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August 13, 2012 2:13:24 AM

Sorry but no.

The M5A97 Pro has 1 full width 16x slot (blue) and one 16x slot (black) running at 4x width.

The link speed may run at 1.1 spec for power saving but should jump up to 2.0 when needed.

The performance difference on a single card is rather minimal between 16x and 4x, even less so when one card is in crossfire due to the longer frame pitch.
August 13, 2012 3:15:52 AM

is it worth me having this crossfire set-up, it seems to have been great apart from prototype 2 which everyone appears to be having issues with.
August 13, 2012 4:51:24 AM

donohue100 said:
is it worth me having this crossfire set-up, it seems to have been great apart from prototype 2 which everyone appears to be having issues with.


Yes. Crossfire on high end cards is terrific. In the 6000 and 7000 series, crossfire yields are close to 100%
August 13, 2012 2:47:56 PM

Thanks for that I had begun to think I had wasted my money. My 3d marks with the xtra card is almost double. However prototype 2 shows no improvement and runs worse. Max payne 3 also shows no fps improvement.
August 13, 2012 3:12:27 PM

donohue100 said:
Thanks for that I had begun to think I had wasted my money. My 3d marks with the xtra card is almost double. However prototype 2 shows no improvement and runs worse. Max payne 3 also shows no fps improvement.


Yeah it's a very game by game metric. Crossfire works once AMD tweaks it for each game. Sometimes they're ahead of the curve, other times they're behind it. Make sure that you have the latest CAP profiles installed at all times
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