Key term
WJEC A-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
Advanced Data Structures and Logic
Recursion, Sorting and Searching
Programming Paradigms and Translators
Topic overviewFunctional, declarative and imperative paradigmsClasses, methods and object-oriented designStandardisation of computer languagesAmbiguity in natural language and unambiguous notationBackus-Naur form and syntax diagramsCompilers, interpreters and assemblersTranslation and execution errors
System Design and Human-Computer Interaction
Software Engineering Tools and Professional Practice
Topic overviewSoftware tools for the software engineering processSoftware packages in systems analysis and specificationSoftware packages in systems designTesting tools and testing strategiesProgram version managementProgram libraries and project management toolsCodes of conduct and professional behaviour
Advanced Architecture and Assembly Language
Communication Networks and File Organisation
Number Representation and Floating Point
Databases and Distributed Systems
Topic overviewConsistency, redundancy and data independenceRelational organisation and normalisationRestructuring data into third normal formEntity relationship modellingQuery languages and SQLValidation, verification and the DBMSBig Data, data warehousing and miningDistributed systems and distributed databases
Operating System Management
Software Systems and Applications
Data Security, Cryptography and Attack
Number Representation and Floating Point
Sign and magnitude representation
- 3 things to know
- A2 Unit 4
Overview
Recall questions on how the sign bit works, representing −20 and reading 10000111, the range and why it is one value narrower, the two zeros and why they cost, why plain addition fails, and why two's complement displaced it.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
How does sign and magnitude represent a negative number?
Key term
State the range of an 8-bit sign and magnitude number.
Questions from this subtopic
Each one with the model answer underneath.
- 1
How does sign and magnitude represent a negative number?
Model answer
The most significant bit is used as a sign, 0 for positive and 1 for negative, and the remaining bits hold the magnitude.
- 2
Represent −20 in 8-bit sign and magnitude.
Model answer
10010100.
- 3
What denary value is 10000111 in 8-bit sign and magnitude?
Model answer
−7.
- 4
State the range of an 8-bit sign and magnitude number.
Model answer
−127 to +127.
- 5
Give the two representations of zero in 8-bit sign and magnitude.
Model answer
00000000 and 10000000.
- 6
Why is having two zeros a problem for a processor?
Model answer
A comparison for zero must test two patterns, which complicates the hardware and the programmer's logic.
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