Scale-up and scale-out interconnect: PCIe hierarchy and switching, high-speed Ethernet and SerDes, die-to-die and board-level links, copper versus optical at each tier, retimers, connectors and cable plant, topology, oversubscription, and the bandwidth and latency budget for each hop. Expert command of state-of-the-art copper and optical interconnect: PCIe, high-speed Ethernet and SerDes, DAC and twinax, backplane and cabled channels, AOCs, and pluggable or co-packaged optics, with the signal-integrity judgment to know where each approach stops working.