1 additional PCI-Express x1 slot is needed

Re: pcie x4 card in pcie x1 slot You can put smaller cards in a larger slot, but not the other way around So a 1x will fit in a 16x or 8x

PCI-E X16 Slots can run in x1, x4 , x8 and x16 modes so you can install a x1 card in a x16 slot without worries of shorting anything as long as

pcle x1 slot Expansion-Box with 4x PCIe x1 Slots and PCIe x2 Host Card, for short cards up to 20cm

pcle slot If you have the option of multiple slots where at least one supports PCIe, it's worth considering your secondary slot for an SSD upgrade When combined