For instance, there’s one minor pinout hiccup that doesn’t occur ... M-key slots and cards for PCIe up to x4, and B+M cards for PCIe up to x2 and compatibility with both B-key (WWAN) and ...

PCIe x4 and x8 cards can draw up to 25W from the motherboard's slot, while x1 cards are limited to 10W unless configured as a 'full-height' or 'high-power card' to pull the aforementioned 25W.