A truth table shows the output for EVERY possible combination of inputs. With 2 inputs, there are 4 possible combinations (2² = 4).
| AND Gate Truth Table | OR Gate Truth Table | NOT Gate Truth Table | |||||
|---|---|---|---|---|---|---|---|
| A | B | Q (A AND B) | A | B | Q (A OR B) | A | Q (NOT A) |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
| 0 | 1 | 0 | 0 | 1 | 1 | 1 | 0 |
| 1 | 0 | 0 | 1 | 0 | 1 | ||
| 1 | 1 | 1 | 1 | 1 | 1 | ||
AND Gate: Only ONE row outputs 1 (the last row: 1,1 → 1). All need to be true!
OR Gate: Only ONE row outputs 0 (the first row: 0,0 → 0). At least one needed!
NOT Gate: Just FLIPS the bit - 0 becomes 1, 1 becomes 0
This key facts covers Truth Tables - All Possible Combinations 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 6 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 | |