What is PCIe? Understanding PCIe Slots, Cards and Lanes

Why do internal > external SAS expanders require a PCIe slot? pcie slot function PCIe compatibility and performance generates a LOT of confusion In Explaining PCIe Slots pcie 40 gpu in 30 slot So a pcie x8 card will fit in a pcie x8 and pcie x16 slot, but will not fit in a pcie x4 or pcie x1 slot Definition feels contradictory (

pcie x4 in x16 slot Figure 2 The standard PCI Express slot sizes on computers today are x1, x4, x8, and x16 Software compatibility is also ensured by the PCI