Key term
WJEC AS-Level Computer Science 601-5345-3
Hardware: Architecture, Memory and Storage
Networks and Data Transmission
Logic Gates and Boolean Algebra
Data Representation and Data Types
Data Structures
Organisation of Data: Files and Records
Database Systems
The Operating System
Algorithms and Programs
Principles of Programming
Systems Analysis
Software Engineering and Program Construction
Topic overviewIntegrated development environments and their purposeEditors, syntax highlighting and code entry toolsDebugging tools: breakpoints, stepping and watchesTranslation, source code and object codeLexical analysis and the symbol tableSyntax and semantic analysisCode generation and optimisation
Types of Software System
Practical Programming
Data Security and Integrity
Computing, Society and the Law
Topic overviewSocial and economic change from computingComputers and the nature of employmentThe digital divide and cultural changeEnvironmental cost of computingData protection and freedom of information lawThe Computer Misuse Act 1990 and computer crimeCopyright, surveillance and professional codes
Logic Gates and Boolean Algebra
- 7 subtopics
- 21 things to know
- AS Unit 1
What Logic Gates and Boolean Algebra covers
Logic Gates and Boolean Algebra is examined in AS Unit 1, Fundamentals of Computer Science. It covers logic gates and their truth tables, Boolean notation and expressions, building and reading truth tables, Boolean identities and rules, simplifying Boolean expressions, De Morgan's laws and masking and clearing registers.
Where it is assessed
AS Unit 1
Fundamentals of Computer Science, examined again at A2 at a more demanding level.
Check the WJEC specification ↗The 7 subtopics
Each one has its own page. WJEC AS Computer Science students sit this topic in the first year.
- Logic gates and their truth tablesRecall questions on when AND, OR, NOT and XOR each output 1, the four rows of each two-input truth table, the one case where OR and XOR disagree, everyday situations that behave like each gate, and why XOR is the natural way to compare two bit patterns.Open →
- Boolean notation and expressionsRecall questions on how AND, OR, NOT and XOR are written, why AND is written like multiplication and where the addition analogy breaks down, operator precedence, evaluating expressions, writing one for an alarm circuit, and why brackets matter.Open →
- Building and reading truth tablesComplete truth table of A·B + ¬A and complete truth table of ¬(A·B).Open →
- Boolean identities and rulesTwo identity laws, two annulment laws and two idempotent laws.Open →
- Simplifying Boolean expressionsRecall questions on why simplification is worth doing before a circuit is built, the absorption, complement and distributive laws applied to worked expressions, factorising, and what A ⊕ A, A ⊕ 0 and A ⊕ 1 reduce to.Open →
- De Morgan's lawsProcedure for applying De Morgan's laws to an expression and most common mistake made when applying De Morgan's laws.Open →
- Masking and clearing registersRecall questions on what a mask is, which operation isolates, sets or inverts chosen bits and what each mask must contain, worked AND, OR and XOR calculations in binary, clearing a register two ways, and testing one bit.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Evaluation
How is XOR written in Boolean notation, why is AND written as multiplication, and how are two mixed expressions evaluated?
Key term
State the four rows of the truth table for a two-input AND gate.
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For the expression A·B + ¬A, what is the output when A = 0 and B = 0?
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State the two identity laws.
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Why is it worth simplifying a Boolean expression before building the circuit?
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What is a mask?
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State the four rows of the truth table for a two-input OR gate.
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How is the OR operation written in Boolean algebra?
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For the expression A·B + ¬A, what is the output when A = 1 and B = 0?
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State the two annulment laws.
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Simplify (A + B)·(A + ¬B).
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State De Morgan's law for a negated AND.
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Which operation isolates chosen bits, and what should the mask contain?
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State the four rows of the truth table for a two-input XOR gate.
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What symbol is conventionally used for XOR?
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For the expression A·B + ¬A, what is the output when A = 1 and B = 1?
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State the two idempotent laws.
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What does A·¬A + B reduce to?
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State De Morgan's law for a negated OR.
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What mask extracts the lower four bits of a byte, and what happens to the rest?
Take Logic Gates and Boolean Algebra further
The same content, four other ways.
Questions from this topic
Each one with the model answer underneath.
- 1
Under what condition does an AND gate output 1?
Model answer
It outputs 1 only when every one of its inputs is 1, and 0 in all other cases.
- 2
Under what condition does an OR gate output 1?
Model answer
It outputs 1 when at least one of its inputs is 1, and gives 0 only when all of them are 0.
- 3
What does a NOT gate do?
Model answer
It takes a single input and outputs the opposite value, turning a 0 into a 1 and a 1 into a 0.
- 4
Under what condition does an XOR gate output 1?
Model answer
It outputs 1 when its two inputs are different, and 0 when they are the same.
- 5
State the four rows of the truth table for a two-input AND gate.
Model answer
Inputs 0 and 0 give 0, inputs 0 and 1 give 0, inputs 1 and 0 give 0, and inputs 1 and 1 give 1.
- 6
State the four rows of the truth table for a two-input OR gate.
Model answer
Inputs 0 and 0 give 0, inputs 0 and 1 give 1, inputs 1 and 0 give 1, and inputs 1 and 1 give 1.
What is inside Levo
Six ways to work the same material.
Logic Gates and Boolean Algebra revision questions
- Is Logic Gates and Boolean Algebra examined at AS in WJEC Computer Science?
- Yes. It sits in AS Unit 1, which you take in the first year, so it is on the AS paper as well as counting towards the full A level.
- What does Logic Gates and Boolean Algebra cover in WJEC AS-Level Computer Science?
- 7 subtopics: logic gates and their truth tables, boolean notation and expressions, building and reading truth tables, boolean identities and rules, simplifying boolean expressions, de morgan's laws and masking and clearing registers. Each one has its own page with questions and model answers.
- How is Logic Gates and Boolean Algebra organised?
- By the WJEC 601-5345-3 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Logic Gates and Boolean Algebra, on a schedule.
Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.
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