Before the personal computer, operation controllers had PLCs, programmable logic controllers, to manage what machinery was doing. Now we have PACs and IPCs to add to the mix, and the confusion over which does what and where each is best grows.
A PLC is the origin of control specific machinery, built to last through extreme environments and relaying on/off instructions to machinery based on input from sensors. The most applicable situation is amusement park rides. An operator pushes the command to execute the ride, and the PLC takes over from there. Some can be as simple as automating the order of events of one precise schedule, and some can manage variables to adapt the schedule as needed.
PACs are programmable automation controllers, and these do much the same as PLCs but without the option of inputs. A PLC can function as a PAC, but usually the reverse is not true.
An IPC is an industrial personal computer, and these carry out much more computationally heavy tasks. One common situation that IPCs excel at is mixes of materials that vastly change properties at different ratios.
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