# The Port and Node System¶

One of the key structural improvements made to Finesse is the introduction of a flexible port and node system. This system underpins the code structure of Finesse as all couplings and interactions are performed via ports and nodes of components.

A Port in Finesse 3 is fundamentally similar to the definition of a node in Finesse 2; i.e. it represents a point of connections at any arbitrary component. These connection points are then Node instances which represent the direction of the coupling into/from the component and also the type of the connection. This connection type is a new feature for Finesse 3 as previous versions only allowed optical nodes at a component and in a model, whereas Finesse 3 has three different node types (see NodeType) - optical, electrical and mechanical - with inter-couplings allowed between these different nodes.