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.
Truth Tables - All Possible Combinations
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
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 | |