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Motherboards and PCI-E slots...

Discussion in 'Motherboards & Memory' started by hat, May 23, 2010.

  1. hat

    hat Maximum Overclocker

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    A lot of boards say that they have two pci-e x16 slots, but they run in 8x mode when running crossfire/sli. My friend is upgrading and we're looking at some boards to suit him, since he has a pci-e x1 sound card. Most motherboards have the top slot being a pci-e x16 slot. We would like to run the sound card above the graphics card so it's not restricting the gpu airflow any.

    Does this 8x mode when in crossfire/sli mean that the second slot is only 8x electricially, or does it mean that they're both electricially x16 slots, but they drop to 8x mode?
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  2. theonedub

    theonedub habe fidem

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    A lot of boards actually have a 1x slot at the top usually right next to the northbridge for sound cards, tuners, etc.

    The answer to your question depends on the board and chipset. For example, on my P55 SLI, the two x16 slots run x8 when dual GPUs are in use and x16 on the primary when only one card is used. The 1x slots are run off the SB and do not affect the two x16 slots.
    hat says thanks.
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  3. hat

    hat Maximum Overclocker

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    What about the second slot? Would it run in x16 when only one slot is used?

    Yes, I know a lot of boards have the pci-e x1 slot on top. My board does, and the one I reccomended to him does. I'm just asking for my own knowledge.
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  4. theonedub

    theonedub habe fidem

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    When I was rearranging my 275s I tried using the second slot and leaving the top empty, the board did not boot without the GPU in the Primary. What board are you looking at? Unless its an AMD board with an integrated GPU I think the same thing will apply.
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  5. hat

    hat Maximum Overclocker

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  6. boulard83

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  7. hat

    hat Maximum Overclocker

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    It's already ordered.

    He's just a gamer, he's not a hardcore overclocker or enthusiast, so I think he'll be fine with the 770 board.
    Crunching for Team TPU
  8. boulard83

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    I tend to go with the latest when i buy new stuff ... its changing so fast that if you order older, your already way behind and the board i listed arnt pricey.

    Can you change your order ? if its not yet processed you can change it.
  9. Hockster

    Hockster

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    My Maximus Formula came with a PCIEX1 audio card that only worked in the top slot. It would overheat and crap out from the heat from the 4890 that was just below it.
  10. mastrdrver

    mastrdrver

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    It depends on the board. Most of the times I think the bottom slot is only 8x. Some of the more expensive boards that do 8x/8x for crossfire/sli will also do 16x for the 2nd slot but not many. Some like Asus' new 890gx board will do 16x in the bottom slot but you have to put a card in to the unused slot or else you'll only get 8x.

    If you're unsure, just go to the manufacturers website and download the manual. There is always a comment about it in there.

    Also, if you put some other PCIe card in to the second slot (whether it is 1x like a sound card or longer doesn't matter) the top slot will switch to 8x. I've seen DFI and Gigabyte offer options in the bios to change that to allow 1x to the second slot and 16x to the top. That is rare though.
  11. DriedFrogPills

    DriedFrogPills New Member

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    afaik it depends on the board, a lot of p55 the second x16 mechanical is only ever x8 electrical so it can never run at x16 electric, its is something that they do bury in the spec mobo makers
  12. Wile E

    Wile E Power User

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    I think the main thing hat was trying to ask is this:

    If you have a board that has 2 gfx slots, and is an 8+8 board in Crossfire/SLI, does putting a sound card in the second slot turn the first slot into a 8x slot.
  13. DriedFrogPills

    DriedFrogPills New Member

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    yes it does, but they won;t have that problem with the board he has ordered
  14. Bjorn_Of_Iceland

    Bjorn_Of_Iceland

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    Yes it will make it 8x.
  15. RejZoR

    RejZoR

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    Boards that use Intel X48 and X58 chipsets can utilize full 16x mode when cards are in SLi/Crossfire (so both cards have 16x each). All the other chipsets divide 16x lane into 8x for each.
  16. Mussels

    Mussels Moderprator Staff Member

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    what it means is that the slots are 16x in length, but electrically it runs as 16x/0x or 8x/8x - they share the lanes.

    its not often a good idea to put a video card in anywhere but the primary slot, as some motherboards wont boot in that situation (they SHOULD, but some just dont)


    edit: and doesnt the AMD 770 boards use 16x/4x? in which case its a bad idea to have GPU in secondary slot.
  17. Bo$$

    Bo$$ Lab Extraordinaire

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    not all, my 750i SLI goes 16X and 8X when both are populated, and my brothers P35 go 16X and X4 (which sucks ass!) when both are populated , but it really depends on the chipset and yes mussels does AMD770 goes 16X and X4 (until it breaks that is :() ;)
  18. Mussels

    Mussels Moderprator Staff Member

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    P35 doesnt have switching, its permanently 16x/4x
  19. Bo$$

    Bo$$ Lab Extraordinaire

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    sorry thats what i meant :rolleyes:
  20. Zubasa

    Zubasa

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    The 790FX and 890FX does 16x+16x CF or 8x+8x+8x+8x CF or other wierd combos depends on the board ;)
  21. RejZoR

    RejZoR

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    I wouldn't expect anything less than that from such new chipsets. The reason why i was disappointed by P55.

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