On a motherboard spec, what does the x8 mean in "1 x PCIe 3.0 ...
Similarly, you can put a PCIe x8 card in a PCIe x4 slot, but it will operate at half the maximum bandwidth of a PCIe x8 slot.
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If it's a pci-e x1 card, plug it in any black pci-e x1 slot or the bottom pci-e x16 slot (yes, you can put a pci-e x1 or x4 card into a x16 slot), it makes no difference.
5Can I put a PCIE SSD in a PCIEx1 slot? : r/buildapc
Is a free x4 slot enough (if the spec of the drive says PCIe x4, for instance) ... If not, you can still use a NVME SSD for storage by using an adapter card to place it in a regular PCIe slot.