Crossbar

Beginner

A switchboard that can connect any part of the chip directly to any other part at the same time.

Novice

A switch that connects any of $n$ inputs directly to any of $m$ outputs in one step, so transfers that don’t want the same output can happen at the same time.

Expert

Its area and wiring grow roughly with $n \times m$ connection points, so crossbars stay small: inside network routers, or joining a handful of high-bandwidth blocks. Larger systems use a network of smaller switches.

Explained in Architecture (Design Flow).