The basic architecture of a PLC is important to understand. It is crucial to know about the basic PLC hardware components that are inside PLC, because it will make your understanding of the PLC much easier. The hardware components are the physical building blocks of the PLC.
Now, that we know what hardware is inside the PLC, the next step will be to take a look at the software inside the PLC and how it runs. Every PLC has a scan time and a scan cycle. This is how the PLC and the software inside the PLC works. The scan cycle is the cycle of which the PLC gathers the inputs, runs your PLC program and then updates the outputs. This will take some amount of time often measured in milliseconds or ms. The amount of time it takes for the PLC to make one scan cycle is called the scan time of the PLC.