Programmable logic control and synchronous link control are two terms used in computer programming for different types of electronics systems. The two types of control systems are both designed to make automation easier in the industries where they are typically utilized. PLC and SLC systems have central processing units and an input-output interface system. The CPU controls the processes in each but does so through the input and output system that connects to the device it controls. Aside from the general purpose of increased automation control, PLCs and SLCs have some significant differences.