Powerful processors drawn from the PC world and more sophisticated operating systems have made it possible for PACs to operate in various modes and with different deterministic speeds. PACs combine Real-Time Operating Systems (based on Windows CE 5.0 or its successors) with the ability to conduct multiple loop operation, and handle execution priorities in a much more sophisticated manner than a PLC, but with all of the deterministic reliability and safety by means of built in system triggers and a more useful and complex way of handling I/O and system timing. This makes it possible to have both deterministic safety, reliability and speed of the PLC combined with the reliance and power on COTS and standards-based products of the PC. The automation applications of modern controller have emerged as the PAC.
Many end users and OEMs of automation systems and controls work in more than one domain. For instance, even a highly process oriented plant such as a pharmaceuticals manufacturer or a fine chemical manufacturer has requirements within the plant for motion control, inventory management, packaging, and automated identification systems, as well as continuous and batch process control requirements.
The need to integrate LIMS (Laboratory Information Management Systems) and PAT (Process Analyzer Technology) Initiatives, and sampling initiatives around the plant have made it necessary to network multiple domains. In addition, increasing emphasis on conformance and quality management systems as well as the need to conform to increasingly detailed requirements for records and validation, such as the U. S. government's 21 CFR Part 11 and the Sarbanes-Oxley Act, have made companies' desire for fewer and more networkable systems grow in intensity.
A PAC can be used as a wide variety of applications in a wide set of domains within the manufacturing enterprise from inside the facility management system, in the environmental monitoring and handling system, in the factory automation systems themselves, and in the networks necessary to transfer the data from the plant floor and auxiliary control systems to the automation software and control centers and from there to the enterprise management systems themselves.