Cables and connectors

NVIDIA has a fantastic reference guide for high-bandwidth cables and connectors: NVIDIA Cable Management Guidelines and FAQ.

Of note,

Transceiver	Signals	Applications
QSFP56	4x50G	HDR InfiniBand 200G/400G Ethernet
QSFP-DD	8x25G (NRZ) 8x50G (PAM4)	200G Ethernet Slingshot
OSFP	8x25 8x50 8x100	NDR InfiniBand