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 âĻ 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 (0â1, 1â0)
- Symbol: Triangle with small circle (bubble) at output
- Expression: Q = NOT A (or ÂŽA or Ä)
- Real example: Fridge light turns on when door is NOT closed (i.e., when open)
Memory trick: NOT = "Negates/Opposite of This"
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.
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 | |