A desktop PC has a few USB ports on the rear of the system, be it a custom DIY build or a prebuilt turnkey model from the likes of MSI, Asus, Dell, and other vendors. But some may not know that a PC will have a USB header or two inside the chassis. Turnkey systems may have one or none, depending on the model and price, but almost all consumer-grade motherboards purchased standalone will have at least one USB header, though usually more. The primary use for these is to connect USB ports on PC cases.