Interconnect is the network fabric connecting compute nodes (or sockets within a node) in a parallel system. It moves data between processors and is characterized by two independent metrics: latency (fixed time to get any message across) and bandwidth (sustained rate of large transfers).
Workloads are either latency-bound (many small messages) or bandwidth-bound (large bulk transfers), and interconnect optimization focuses on the dominant regime.
Fat tree vs torus topology trade-offs.
Fat tree: hierarchical switches, flat worst-case latency, higher cost Torus/Mesh: direct nearest-neighbor links, scales cheaply, hop count grows with size