GCSE Computer Science (AQA)

Topic Summaries

ALGORITHMS AND PROGRAMMING: Boolean logic

Logic gates and symbols

  • Boolean logic is used in computer systems to make decisions using only two states: 1 = True, and 0 = False. 
  • It is based on logic gates and Boolean operators: AND, OR, and NOT. These are used in logic diagrams, truth tables, and real-world decision-making in code and digital circuits.
Operator Description Symbol (logic gate)
AND True only if both inputs are true
OR True if at least one input is true
NOT Reverses the input (True becomes False, and vice versa)
  • Logic diagrams show how logic gates are connected. You need to be able to: 
    • Recognise AND, OR, and NOT symbols.
    • Draw diagrams from expressions.
    • Trace how inputs flow through each gate.
  • Tip: work from left to right and evaluate gate-by-gate when solving a diagram.
  • Alternative notations you may see:
Symbol Meaning
∧ AND
∨ OR
¬ NOT
T True (1)
F False (0)

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