What is the difference between half-duplex and full-duplex?

Half-duplex communication allows data to flow in both directions but only one direction at a time — like a walkie-talkie. One party transmits while the other listens, then they switch. Ethernet hubs operate in half-duplex — only one device can transmit at a time on a segment, and collisions can occur (managed by CSMA/CD). Full-duplex allows simultaneous transmission in both directions — like a telephone. Modern Ethernet switches operate in full-duplex, eliminating collisions because each switch port has a dedicated path. Full-duplex effectively doubles the available bandwidth compared to half-duplex on the same link (e.g., a 100 Mbps full-duplex link can simultaneously send and receive 100 Mbps each). Modern networks almost universally use full-duplex since hubs have been replaced by switches. Duplex mismatch (one side full, other half) causes poor performance and high collision rates.