Programmable logic controllers are categorized according to

• A. Brand
• B. Number of I/O points
• C. Operating System
• D. CPU Speed

Answer: (B)

The main idea is sizing PLCs by how many I/O points they can handle. This matters because the number of inputs and outputs determines how many sensors, switches, and actuators the controller can directly manage, and it drives the selection of the base unit plus any expansion modules. That’s why PLCs are commonly discussed in terms of small, mid, or large based on total I/O capacity—the category reflects the scale of the control task you’re planning. While brand, operating system, and CPU speed influence other aspects like compatibility and performance, they don’t define the category in the same direct way, since a single brand can offer devices across a wide range of I/O counts and CPUs can be matched to different I/O needs. So, the standard way to categorize PLCs for planning and sizing is by the number of I/O points.