Explain global and detailed routing in physical design.

Global routing: Divides chip into global routing cells (GCells), plans rough wire paths, assigns nets to GCells without exact tracks, focuses on congestion management. Detailed routing: Routes nets on exact metal tracks within GCells, handles design rules (spacing, via rules), uses track assignment and maze routing algorithms. Routing layers: Lower metals for local connections, upper metals for global signals. Considerations: Antenna rules, via minimization, crosstalk, and timing. Modern routers are timing-aware and use multi-threaded algorithms for speed.