A packet switch has a switching unit (SU) for switching packets between network links and a computing unit (CU) connected to the SU through a network link for implementing software control functions over the SU. The SU is formed of different functional components interconnected by generic buses. The components communicate with one another using program data units (PDUs) that are formatted and transmitted according to a shared device protocol. The communication between the components occurs by placing PDUs in bus frames that are passed from component to component. Information is exchanged between the components by adding information to or dropping information from the fields of the PDUs, or by concatenating new fields to the PDUs, as the frames pass from component to component. By using a generic bus to implement PDU-based interconnections within the SU, all the components are forced to support a common interface. Changes to the implementations of any component's interface can thus be accommodated by changing the PDU format as opposed to changing the interfaces of connected components. The new packet switch architecture decouples the components on the switch so that they can be upgraded or otherwise modified independently of one another.