What are the expansion slots on the OptiPlex 7090 SFF and what should I watch out for?

The OptiPlex 7090 SFF has three slots: one PCIe x16 slot (physically x16 but electrically x4 only), one PCIe x4 slot, and an M.2 2230 key E slot for Wi-Fi. That x16/x4 gotcha limits GPU options — stick with low-power cards.