Why do internal > external SAS expanders require a PCIe slot?

Node Duo - Thunderbolt 3 PCIe expansion chassis for 2 cards external pcie slot Host Adapters ; Computer Platform Requirements, Desktop computer equipped with a PCIe x16 slot ; Power On Switch, Wafer Connector; Pitch= (only external gpu slot This adapter enables you to connect external Mini SAS HD devices to a PCIe x16 Gen4 slot, expanding the capabilities of your system It provides a seamless

blackjack european slot The PROBLEM: You want more PCIe Ports for Fitment of Expansion Adapters (Wifi Card, 10GbE