ISO 16484-2:2004 specifies the requirements for the hardware to perform the tasks within a building automation and control system (BACS). It provides the terms, definitions and abbreviations for the understanding of ISO 16484-2 and ISO 16484-3. ISO 16484-2:2004 relates only to physical items/devices, i.e. devices for management functions, operator stations and other human system interface devices; controllers, automation stations and application specific controllers; field devices and their interfaces; cabling and interconnection of devices; engineering and commissioning tools. ISO 16484-2:2004 shows a generic system model to which all different types of BACS and their interconnections (BACS network) can fit. A graphical concept of the BACS network in terms of LAN topology will be provided in ISO 16484-5.