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Does a x4 PCIe mechanical work in a x16 slot in x4 mode?

I know I can place a smaller card in a larger slot. But can I be 100% certain that it works? (if we ignore a broken card or broken slot)

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Simon Verbeke
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  • It's slightly different though. Are there any cases where it won't work if you put a smaller card in a larger slot? – Simon Verbeke Dec 11 '11 at 18:43
  • Smaller cards are intended to be used in larger slots, as part of the PCIe specification. (a 1x card can fit, and operate, in a 1x, 4x, 8x or 16x slot). I'm not sure why you think the linked question is different, he also wants to know if a 4x card will work in a 16x slot, and run at 4x. :) – Ƭᴇcʜιᴇ007 Dec 11 '11 at 18:48
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    Alright, this can be closed then. I though that maybe in some special cases there might be a problem. – Simon Verbeke Dec 11 '11 at 18:53
  • Moreover you can get motherboards with x16 physical slots and less (x8, x4, x1) electrical connectivity. This will also work. Of course if you put a graphics card in such a slot the performance will be poor! – Ben Jackson Dec 11 '11 at 22:11

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Yes, a PCIe x4 card will function in a PCIe x16 slot. The slot will simply use 4 of the 16 lanes available, and the card will work properly. See Wikipedia for more details.

bwDraco
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  • In the specification of the national instrument pcie 6738 (https://www.ni.com/documentation/en/analog-output-device/latest/specs-pcie-6738/specs/), on the foot note 6, you can read:"6 Some motherboards reserve the x16 slot for graphics use. For PCI Express guidelines, visit ni.com/info and enter the Info Code PCIExpress.". Then how can we know of it will be compatible on the slot x16 on my motherboard? – Rémi Baudoux Nov 16 '20 at 08:49
  • it might not work: https://superuser.com/questions/1602514/can-we-connect-pciex4-card-in-pciex16-slot/1607600#1607600 – Rémi Baudoux Dec 05 '20 at 19:20