in theory you can run as much as 16+8 graphics cards on mining boards. but generally you wont run as much as 24 cards, but running more than 8 is quite common.
some mining boards, especially those were made by biostar, come many pci-e x1 connectors(as much as 12), so you would plug breakout boads on them, changing the interface to something like displayport cables and use them connect to actual graphics cards. mining is about using gpu to do maths, not processing massive amount of data, therefore you dont need that much bandwidth, pci-e x1 is all you need.
