This key facts covers The Three Basic Gates within Logic Gates for GCSE Computer Science. Revise Logic Gates in 3.4 Computer Systems for GCSE Computer Science with 16 exam-style questions and 20 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 4 of 9 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
The Three Basic Gates
1. AND Gate - The "Both Required" Gate
- Rule: Output is 1 ONLY if ALL inputs are 1
- Symbol: D-shape with flat back
- Expression: Q = A AND B (or A ∧ B)
- Real example: Microwave runs only if door is closed AND start button is pressed
Memory trick: AND = "All Need to be true"
2. OR Gate - The "Any Will Do" Gate
- Rule: Output is 1 if ANY input is 1 (one or more)
- Symbol: Curved back, pointed front
- Expression: Q = A OR B (or A ∨ B)
- Real example: Burglar alarm sounds if window sensor OR door sensor is triggered
Memory trick: OR = "One Required"
3. NOT Gate - The "Opposite" Gate
- Rule: Output is the OPPOSITE of input (0→1, 1→0)
- Symbol: Triangle with small circle (bubble) at output
- Expression: Q = NOT A (or ¬A or Ā)
- Real example: Fridge light turns on when door is NOT closed (i.e., when open)
Memory trick: NOT = "Negates/Opposite of This"
Practice questions for Logic Gates
An AND gate has inputs A=1 and B=0. What is the output?
Complete the truth table for an OR gate with two inputs A and B. | A | B | Output | |---|---|--------| | 0 | 0 | | | 0 | 1 | | | 1 | 0 | | | 1 | 1 | |