GTX660 Running Below Max Speed

Discussion in 'Mac Pro' started by matty1551, May 4, 2014.

  1. matty1551 macrumors 6502

    Jul 7, 2009
    I installed a GTX660 a few minutes ago and put it in Slot 2 rather than 1, where my old GFX card was. I figured it might be better temperature wise in slot 2.

    However, the expansion slot utility is coming up and telling me that the card is not running at maximum speed.

    Do I have to use it in slot 1 to get max speed?

    Heres a pic.

  2. tosh.macin macrumors newbie

    May 4, 2014
    I think you do have to use slot 1 from what I remember, at least in the older Mac Pro's. Hmmm. Anyone more knowledgable care to comment?
  3. NOTNlCE macrumors 6502a


    Oct 11, 2013
    DMV Area
    Yes, you do need to run the card in slot 1 to get maximum performance. Slot 1 is the only capable slot of running an x16 PCIe lane. Any other slot will happily run it at 8x provided you use the PCIe utility (which you have pictured) to configure it to run at x8. However, Slot 1 is easily the best choice, as it will yield the best performance (x16 bandwidth) and it is physically a double wide slot, so your card isn't blocking access to another PCIe slot.
  4. h9826790, May 4, 2014
    Last edited: May 4, 2014

    h9826790 macrumors G4


    Apr 3, 2014
    Hong Kong
    Same suggestion, use slot 1.

    As you can see in the PCIe Utility. You choose option 2. That means...

    Slot 1 is x16 lane, which is the default slot for high performance graphic card.

    Slot 2 is x1 lane, the slowest one.

    Slot 3 and 4 are x4 lane. Both run at medium bandwidth.

    If you really need to run both cards, choose the 1st option from PCIe Utility.

    And then put the new card in slot 1, and the old card in slot 4 (It seems you don't have any other card).
  5. matty1551 thread starter macrumors 6502

    Jul 7, 2009

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