What is stored in the process image input file of a PLC?

The process image input file in a Programmable Logic Controller (PLC) serves a crucial purpose in the management of real-time data. Specifically, this file contains the status bits of all the physical inputs connected to the PLC, such as switches and pushbuttons. When an input device changes its state—say a pushbutton is pressed—the PLC records this change in the process image input file, allowing the controller to act upon the new input during its execution cycle.

This functionality is essential for the PLC to accurately reflect the real-time status of all inputs it is monitoring, enabling it to execute the programmed control logic based on the current input conditions. The process image input file facilitates quick access to input statuses, making it vital for timely decision-making and process control.

The other options do not fit the definition of the process image input file. The status bits of outputs are stored in the process image output file, while the operational history and programming code of the PLC are not part of the process image input file. Thus, the answer highlighting the status bits of switches and pushbuttons accurately represents the content of the process image input file.