Single card lower slot still x16?

Discussion in 'Video Cards and Graphics' started by runzwithsizorz, Jan 18, 2013.

  1. runzwithsizorz

    runzwithsizorz Diamond Member

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    With a mobo that has 2 slots, 1 labeled PCIe 3.0/2.0x16 (single at x16 or dual at x8/x8 mode), and the other labeled PCIe 3.0/2.0x16 (at x8 mode).
    For air flow, and aesthetics reasons with a single card set up, can the other slot be used and still retain x16? If not, then why the hell is it labeled x16?
     
  2. Termie

    Termie Diamond Member

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    No. You can confirm this simply by running GPU-z with the card installed, which will tell you the speed of the PCIe link.

    Don't know why it's labeled as x16, but the second slot will always be x8. If you're running a PCIe 3.0 card, it won't be a bottleneck. Even for a fast PCIe 2.0 card the bottleneck won't be that significant.
     
  3. KingFatty

    KingFatty Diamond Member

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    It's nothing to worry about if you are at x8. You could even try back-to-back benchmarks.

    Would you mind if your card dropped from 100 fps at x16 down to 99 fps at x8?
     
  4. runzwithsizorz

    runzwithsizorz Diamond Member

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    So obviously I have so much to learn. But I thought that there were some mobos that had 2, or 3 slots with full x16 though-put? So are you saying that if I use that *other* slot, (not as cramped, and more air flow), I will not notice any difference?
    7870 on a Asus p8z77 v pro. A gaming build for Mz Runz :wub:
     
  5. Termie

    Termie Diamond Member

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    PCIe 3.0 x8 bandwidth will be more than sufficient for a 7870.
     
    #5 Termie, Jan 18, 2013
    Last edited: Jan 18, 2013
  6. runzwithsizorz

    runzwithsizorz Diamond Member

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    Thankz, but someday I hope to learn the why's. I have been out of the loop for quite a spell. For me, I do not just want to assemble, I want to learn why this, or that works. Alas, the Mz is growing impatient waiting so my education will have to wait. 2 of the components used in her build is the p/p CM hyper212 plus, and the Seasonic x-650, so perhaps I am doing something right :rolleyes:
     
  7. Termie

    Termie Diamond Member

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    This article should help clear some things up for you: http://www.anandtech.com/show/5458/the-radeon-hd-7970-reprise-pcie-bandwidth-overclocking-and-msaa

    And yes, those are some nice parts you have there. ;)
     
  8. lopri

    lopri Elite Member

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    Check your motherboard's manual. There should be block diagram and instructions on how on-board PCIe slots are configured. Every boards are different, so you should make sure what's what.

    I've been doing for a long time what you're planning to do. If something doesn't work as expected (i.e. nearly identical performance), the most likely fault lies on the board. Then the chipset/video drivers.
     
  9. lehtv

    lehtv Lifer

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    Why do you think airflow would be improved by having the card in the lower slot?

    I would guess it's because the slot is physically capable of x16, but electrically limited to x8
     
  10. Ben90

    Ben90 Platinum Member

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    All three of my physical x16 slots are electrically x16. Not sure where you are getting your info from.
     
  11. infoiltrator

    infoiltrator Senior member

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    I believe 2011 Motherboards support multiple X16 usage.
    For Sandy Bridge/Ivy Bridge the number of lanes available is limited by the on chip control.
    Some motherboards use additional on board support I think?
    Anyway looking at the solder side of the motherboard x16 slot with all contacts soldered does x16, when a section is absent, it is x8, have not checked x4.
    FWIW 3.0 x16 carries twice the bandwith of 2.0x16 so even a 2.0x16 at x4 will carry an SLI set up (which require 2.0x16 x8 minimum).
     
  12. runzwithsizorz

    runzwithsizorz Diamond Member

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    Would still like to learn more about this, manual did not address this.
     
  13. KingFatty

    KingFatty Diamond Member

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    I've already made a similar change, moving my card from the lower x16 slot to the upper x8 slot.

    The reason is that the lower slot was next to the power supply, so it restricted airflow and also created a pocket of super-heated air (like a dead space without a good way for the hot air to escape away from the cavity between the power supply and the card, toward the rear of the case).

    So my overclocks were limited on the video card; I had to artificially limit my overclock due to heat instability, not to mention my power supply was getting cooked by the video card.

    Anyway, by moving my card to the upper slot, that gave it lots of space and eliminated any dead air, everything circulated nicely, and I got a much better overclock. So even though I went from an x16 slot to an x8 slot, I actually got *better* performance because everything ran cooler and I could achieve higher stable GPU overclocks. The overclock simply dwarfed any miniscule reduction the x8 interface caused.

    But my motherboard is an older Asus 890GX that has this funky setup where the lower slot is x16 and the upper is x8, I don't think most motherboards are like that.
     
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