I'm really rather confused by it all, so I've come up with a question or two:

  1. If I buy a motherboard with a PCIe x16 and PCIe x4 slot and put a graphics card in each, will they both run at x8 speeds due to the x16 being split in half, or will they run at x16 and x4?
  2. If I buy two ATI 6850s (let's simplify it to "top-midrange graphics cards"), will there be a noticeable performance drop from running one of them at x4 speeds. They'll be in CrossfireX (linked).

Sorry if this is the wrong place to ask this question.

  • I think Superuser is the best place to ask this question.
    – Oli Glaser
    Aug 31, 2011 at 18:51

2 Answers 2

  1. The one in the x4 slot won't run at x8; it needs a x8 or x16 slot to do that. They will run at x16 and x4.
  2. Look on a benchmarking site.
  • Thanks very much Brian. This was my though too, but I read about bus sharing and thought that might have an impact.
    – Bojangles
    Sep 7, 2011 at 18:11
  • 1
    There is no bus sharing in PCIe - it's all point-to-point.
    – LawrenceC
    Mar 19, 2012 at 15:01

The one in the x4 slot can't run at x8 speeds. The x4 slot is limited to x4. The slots don't split their speed amongst each other like that.

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