Yes, you can install a 1x PCIe card into a 16x or 4x PCIe slot

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Upstream port: PCIe x8 Edge Finger · Downstream port: Two Internal PCIe Cable Port · PCI Express Switch: 16-Lane, 5-Port PCIe Gen 3

PCI-e slot on your motherboard and these only run at 8x or even 4x speeds, they will still work, but performance can be lower than in a full speed slot  Put it in the top slot which is pci-e 16x compared to the bottom slot at pci-e 4x PCIe x16 slot and that one Here is a

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