A Programmable Logic Controller (PLC) is a rugged industrial computer designed to reliably automate processes. At the heart of every PLC is a well-defined architecture that ensures consistent operation under demanding conditions. This presentation explores the key components of that architecture—including the CPU, memory, input and output modules, and power supply—alongside the scan cycle that dictates how the PLC processes information. By understanding these building blocks, we can see how PLCs achieve the speed, accuracy, and robustness required for modern automation systems.