Key term
Eduqas A-Level Computer Science A500QS
Data Structures: Arrays, Records and Hash Tables
Stacks, Queues, Linked Lists and Trees
Boolean Logic and Simplification
Algorithms, Pseudo-Code and Programming Constructs
Variables, Scope, Parameters and Identifiers
Recursion and Modular Programming
Sorting Algorithms
Searching and Shortest-Path Algorithms
Big O Notation and Algorithm Efficiency
Validation, Verification and Testing
Data Compression
Programming Paradigms and Computer Languages
Topic overviewProgramming paradigms and where each is usedProcedural programmingEvent-driven and visual programmingMark-up languagesObject-oriented programming: objects, classes and methodsAmbiguity in natural language and the standardisation of languagesBackus-Naur form and syntax diagramsHigh-level and low-level languages, and choosing one
Systems Analysis, Maintenance and Documentation
Topic overviewWaterfall, Agile and approaches to systems developmentThe feasibility study, budgets and time scalesMethods of investigationAbstraction, decomposition and data flow diagramsSelecting suitable hardware and softwareAcceptance testing and methods of changeoverPerfective, adaptive and corrective maintenanceBackup and recovery proceduresUser and maintenance documentation
System Design and Human-Computer Interaction
Software Engineering Tools and Translators
Topic overviewSoftware tools for the software engineering processSoftware packages in analysis, specification, design and testingIntegrated development environmentsDebugging toolsProgram version managementCompilers, interpreters and assemblersThe stages of compilationTranslation errors and execution errors
Computing, Society and the Law
Computer Architecture, the Processor and Assembly Language
Topic overviewHardware elements and how they are connectedVon Neumann architecture and the stored program conceptThe processor: control unit, ALU and registersTypes of memory: RAM, ROM and virtual memoryCache memory and locality of referenceThe fetch-execute cycle and its registersParallel processing and the limits to parallelisationAssembly language and executing a program
Input, Output and Secondary Storage
Topic overviewInput devices and how data is capturedOutput devices and how results are presentedChoosing input and output devices for a situationVoice input, dictation and voice print recognitionMagnetic, optical and solid state storageComparing secondary storage for a purposeDisc organisation, fragmentation and defragmentation
Networks, Protocols and the Internet
Topic overviewNetworks, LANs and WANsNetwork topologies and connection hardwareNetworking standards and the layered modelIP addressing, TCP and UDPApplication protocols: HTTP, FTP, SMTP, IMAP and DHCPHandshaking and establishing a connectionWireless hardware and wireless technologiesThe internet and connected mobile devices
Data Transmission and Network Performance
Topic overviewSerial and parallel transmissionSimplex, half duplex and full duplexMultiplexing and sharing a channelCircuit, message and packet switchingPackets, headers and packet contentsNetwork collisions and collision detectionRouting traffic on a networkCalculating transfer rates and lowest cost routes
Number Systems and Binary Arithmetic
Data Types, Characters and Floating Point
Topic overviewPrimitive data typesStorage requirements for each data typeASCII and standardised character setsUnicode and multilingual encodingFloating point form: mantissa and exponentConverting between real numbers and floating pointInteger and floating point comparedTruncation, rounding and accuracy
Files, Records and File Organisation
Topic overviewThe purpose of files in data processingFiles, records and fieldsFixed and variable length fields and recordsMaster files and transaction filesSerial and sequential file accessIndexed sequential access and multi-level indexesDirect access and hashing algorithmsOverflow handling and file reorganisationFile security, backups, generations and archiving
Databases, Normalisation and Entity Modelling
SQL, Big Data and Distributed Systems
Topic overviewQuery languages and the purpose of SQLCreating tables: CREATE TABLE, data types and keysRetrieving data with SELECT, FROM and WHEREComparison operators, IN, AND, OR and sub-queriesSorting, grouping and aggregate functionsInserting, updating, deleting and joining dataThe DBMS, the data dictionary and distributed databasesBig Data, data warehousing, data mining and predictive analytics
The Operating System and Its Modes
Topic overviewThe need for an operating system and the role of the kernelManaging peripherals, processes and memory protectionThe user interface and the layers between user and hardwareDirectory structures and file attributesUtility softwareBatch processing, real time control and real time transaction systemsTypes of operating system: single-user, multi-user, multi-tasking and multi-programmingDesigning an interface for different users and environments
Interrupts, Memory Management and Scheduling
Topic overviewWhat causes an interruptInterrupt handling and the interrupt service routineInterrupt priorities and how they are allocatedPartitioning main memoryMethods of data transfer between processor and devicesBuffers and double bufferingHigh level scheduling, processor and device allocationProcess states, time-slicing, polling and threading
Types of Software System
Data Security, Cryptography and Attack
Topic overviewOnline updating and the integrity of shared filesDangers of holding personal dataClerical procedures, access levels, passwords and write protectionCryptography: its purpose, and symmetric and asymmetric keysHashing, digital signatures and certificatesCaesar and Vernam ciphers and comparing cipher strengthBiometric technologies and their limitationsThreats, damage and contingency planningMalicious software, hacking and penetration testing
Variables, Scope, Parameters and Identifiers
Call by value and call by reference
- 3 things to know
- Component 1
Overview
Call by value and call by reference.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
What is call by reference?
Process
A variable X holds 5 and is passed by value to a procedure that doubles its parameter. What does X hold after the call?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is call by value?
Model answer
Call by value passes a copy of the data into the subprogram. Changes made to the copy do not affect the original variable.
- 2
What is call by reference?
Model answer
Call by reference passes the address of the original variable into the subprogram. Changes made inside the subprogram alter the original.
- 3
A variable X holds 5 and is passed by value to a procedure that doubles its parameter. What does X hold after the call?
Model answer
X still holds 5 because the procedure worked on a copy. The doubled value of 10 is lost when the procedure returns.
- 4
A variable X holds 5 and is passed by reference to a procedure that doubles its parameter. What does X hold after the call?
Model answer
X holds 10 after the call because the procedure worked on the original store. The change is visible to the calling program.
- 5
Give one advantage of call by value.
Model answer
Call by value protects the caller's data because the subprogram cannot change the original. Faults inside the subprogram stay contained.
- 6
Give one disadvantage of call by value.
Model answer
A large structure such as an array is expensive to copy in both time and memory. The copy must be made every time the subprogram is called.
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