What does 4.6 Fundamentals of computer systems cover?

It covers the relationship between hardware and software and the classification of software into system and application software, the role of the operating system and utility programs, logic gates and Boolean algebra including truth tables and simplification, the classification of programming languages by level and paradigm, and the types of program translation (assembler, compiler, interpreter) with the stages of compilation.

What is the difference between system and application software?

System software runs and manages the computer itself, including the operating system, utility programs, device drivers and language translators. Application software lets a user perform a specific task, such as a word processor, spreadsheet, browser or game. The operating system is system software; the programs you open to do work are applications.

What are De Morgan's laws?

De Morgan's laws let you simplify Boolean expressions involving a NOT over a bracket. NOT(A AND B) equals (NOT A) OR (NOT B), and NOT(A OR B) equals (NOT A) AND (NOT B). When you break the bar over a bracket, the operator flips: AND becomes OR and OR becomes AND. They are used to reduce circuits to fewer gates.

What is the difference between a compiler and an interpreter?

A compiler translates the whole program into machine code before it runs, producing a fast standalone executable, but reports all errors only after compiling. An interpreter translates and executes one statement at a time, which is slower and needs the interpreter present, but reports errors as it reaches them, which is good for development. An assembler translates assembly language into machine code.

What are the stages of compilation?

Lexical analysis breaks the source into tokens and removes white space and comments; syntax analysis (parsing) checks the tokens against the grammar and builds a parse tree; code generation produces machine code or intermediate code such as bytecode; and optimisation improves the generated code to run faster or use less memory without changing what it does.

EnglandComputer Science

AQA A-Level Computer Science 4.6 Fundamentals of computer systems: hardware, software, logic gates, languages and translators

A deep-dive AQA A-Level Computer Science guide to 4.6 Fundamentals of computer systems. Covers hardware and software and the operating system, logic gates and Boolean algebra, the classification of programming languages, and the types of program translation including the stages of compilation.

Generated by Claude Opus 4.817 min read4.6Updated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

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What 4.6 actually demands
Hardware, software and the operating system
Logic gates and Boolean algebra
Languages and translation
Check your knowledge

What 4.6 actually demands

This module links the abstract programming world to the physical machine. AQA expects you to classify software, explain what the operating system does, work with logic gates, truth tables and Boolean simplification, classify languages, and explain how source code becomes something the processor can run.

Hardware, software and the operating system

Hardware is the physical components; software is the programs and data. Software divides into system software (operating system, utilities, drivers, translators) and application software. The operating system handles memory management, process scheduling, file management, device management, security and the user interface; utility programs do housekeeping such as backup and defragmentation.

Logic gates and Boolean algebra

Know the gates NOT, AND, OR, XOR, NAND, NOR and their truth tables, build and read combinational circuits, write the matching Boolean expression, and simplify using the laws of Boolean algebra, including De Morgan's laws, to use fewer gates.

Languages and translation

Classify languages by level (machine code, assembly, high-level) and by paradigm (imperative, object-oriented, declarative, functional). An assembler translates assembly to machine code; a compiler translates the whole program at once into a fast executable; an interpreter translates and runs statement by statement. Compilation has four stages: lexical analysis, syntax analysis, code generation and optimisation, sometimes producing intermediate code (bytecode).

Check your knowledge

State the difference between system software and application software. (2 marks)
State two functions of an operating system. (2 marks)
State the output of an XOR gate when both inputs are 1. (1 mark)
Use De Morgan's law to rewrite $\overline{A + B}$ . (2 marks)
State one advantage of a high-level language over machine code. (1 mark)
State the difference between the imperative and declarative paradigms. (2 marks)
State one advantage of an interpreter over a compiler for development. (1 mark)
State what happens during lexical analysis. (2 marks)

Solutions

Q1: System software runs and manages the computer (the OS, utilities, drivers, translators); application software lets the user perform a specific task such as word processing.
Q2: Any two of: memory management, process scheduling, file management, device management, security, providing a user interface.
Q3: 0, because XOR outputs 1 only when the inputs are different.
Q4: $\overline{A + B} = \overline{A} \cdot \overline{B}$ .
Q5: It is easier to write and read and is portable between different machines.
Q6: Imperative programs specify the step-by-step instructions (how); declarative programs specify the desired result (what), leaving the steps to the system.
Q7: It reports errors as it reaches them, statement by statement, making debugging easier during development.
Q8: The source code is broken into tokens (keywords, identifiers, operators) and white space and comments are removed.

Sources & how we know this

AQA A-level Computer Science (7517) specification — AQA (2015)