What are PLCs? What are PACs?

Programmable logic controller (PLC) is a type of industrial computer that makes a decision to help guide or monitor a process, often for factory automation or machine control in discrete applications, although some control processes (continuous, batch or hybrid). A PLC often accepts inputs from sensors and sends instructions to actuators. PLCs have been defined by the number of inputs/outputs they can control and by processing speeds. PLC programming occurs with IEC 61131-3 Programming Languages and some can accept other programming.
A programmable automation controller (PAC) is a type of industrial logic device based on a PC (personal computer) platform.