eGPU External graphics card
A desktop graphics card in an external enclosure, connected to a laptop over Thunderbolt or OCuLink. Gives thin machines desktop gaming performance while they sit on the desk.
The bottleneck is the connection. Thunderbolt 3 and 4 provide PCIe 3.0 ×4, roughly a quarter of the bandwidth a card gets in a real slot, which typically costs 10–30 percent of performance — more if the image has to travel back to the built-in display instead of a monitor plugged into the card. Thunderbolt 5 and OCuLink raise the ceiling considerably; OCuLink passes PCIe straight through and loses almost nothing, but offers no hotplug and no power delivery. Apple removed support entirely with Apple Silicon. The economics are questionable: the enclosure costs about as much as a mid-range card. It has found new relevance through handheld gaming PCs.