The “Brains” of a machine, a PLC is a digital computer used for the automation of industrial processes, such as control of machinery on an assembly line. They are programmed to operate in a very reliable specific fashion (turning on and off outputs) based on inputs, timers, and other internal logical controls. Early PLC’s were designed to replace electromechanical relay logic, and the basic programming structure of ladder logic’s “contacts and coils” is a holdover from those electrical diagrams. Today there are a wide range of PLC hardware options, from very simple “smart relays” to very complex, factory-wide control platforms. Commonly a user will choose a hardware platform based on the number and type of inputs and outputs they need for a machine, along with functions for data-storage, security, and communications.