6. SI and the IT system

The IS organizes the cooperation between the PLC and human work. The physics of the PLC, which resides entirely in the IT system, is expressed in terms of memories, processors, software and networks.

The definition and control of the IT system are the domain of specific techniques, different from those we have just described for the IS. However, IS design cannot ignore them: its requirements must be formulated in terms that IT can take into consideration.

Data volume and performance requirements (processing and display times) are matched by resource sizing (database size, transactional monitor and processor power, network throughput). The architecture of operating systems, programming languages, software components and algorithms responds to the complexity of processing.

Firewalls and "demilitarized zones" protect...