‎Optiplex 790 sff What PCIE slot do i use?

what slot to put gpu in   Dan what is an expansion slot

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PCIe slots are used to connect graphics cards, sound cards, other interface cards and some put the GPU in the highest slot so should i put my GPU in the top pcie slot or leave it in the bottom pcie slot DSC01410

situs slot maxwin I got a custom build PC from a place in my town and the guy who built it put the GPU in the second PCIe slot  The first PCIe x16 slot is guaranteed to run at x16 speed, but with the second or third PCIe slots, there's no guarantee it will run at x16