PLC / PAC's - A PLC (programmable logic controller) is a programmable microprocessor-based device that is used in automation and manufacturing to control assembly lines and machinery on the shop floor as well as many other types of mechanical, electrical, and electronic equipment in a plant.
A PAC (programmable automation controller) is a programmable microprocessor-based device that is used for discrete manufacturing, process control and remote monitoring applications. The term was coined to accommodate for better real-time control needed in some automation applications.