What does the binary number system refer to in PLC context?

• A. A base 8 numbering system
• B. A decimal system with 2 digits
• C. A hexadecimal system
• D. A base 2 numbering system meaning only the digits 0 and 1 are used

Answer: (D)

In PLCs, binary refers to a base-2 numbering system that uses only two symbols: 0 and 1. This mirrors how digital hardware operates—each bit represents a discrete state, off (0) or on (1). Because PLCs control real-world devices, those binary states map directly to inputs, outputs, and memory bits, making it natural to model logic with true/false or on/off conditions. Grouping bits into bytes or words lets you represent more information or address specific memory locations, while still keeping the underlying hardware behavior rooted in two states. Other numeral systems exist to compactly express binary data (like octal or hexadecimal), but the actual operation and representation of discrete PLC signals rely on base 2 with digits 0 and 1.