## Learning Outcomes

- Define **software** and explain how it differs from hardware
- Distinguish clearly between **system software** and **application software**
- Identify the four main categories of system software: operating systems, utilities, libraries and translators
- Classify common examples correctly in exam questions
- Explain why each type of software is needed in a working computer system
- Compare compilers, interpreters and assemblers accurately using precise terminology

## AQA A-Level Computer Science (7517) Syllabus

For the AQA A-Level Computer Science (7517), you are expected to understand software classification within computer systems, with a focus on the following syllabus points:

- Know that software is classified into **system software** and **application software**
- Explain what is meant by **system software** and **application software**
- Identify the main forms of system software: **operating systems**, **utility programs**, **libraries**, and **translators**
- Understand why system software is needed to support the running of the computer system
- Recognise that application software is used to help the end user perform tasks
- Distinguish between different translators: **compiler**, **interpreter**, and **assembler**
- Classify given examples of software accurately using exam-safe terminology
- Understand the link between software classification and the wider role of the operating system

## Test Your Knowledge

_Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, look more closely at that area during your revision._

1. What is the difference between system software and application software?
2. Name the four main types of system software in the AQA specification.
3. Why is a translator needed before a CPU can run most source code?
4. Is a web browser system software or application software? Why?
5. How does an assembler differ from a compiler?

## Introduction

A computer system only works when **hardware** and **software** operate together. Hardware gives the machine its physical parts, such as the processor, memory and storage devices. Software gives those parts instructions so that inputs can be processed and outputs can be produced.

For this topic, the key exam skill is not just recalling examples. You need to classify software correctly and explain its purpose. Many students know what a browser or antivirus program does, but lose marks because they cannot say whether it is **application software** or **system software**, or because they confuse the operating system with every other background program.

> **Key Term: software**
> The programs and instructions that run on a computer system.

### Hardware, software and the need for classification

Software is grouped into categories because different programs do different jobs in a computer system. Some software exists mainly to help the **user** complete a task. Other software exists mainly to help the **computer system** run properly.

That distinction gives the two broad classes:

- **system software**
- **application software**

This may look simple, but exam questions often test the border between them. A useful way to think about it is this:

- If the main purpose is to support the running, maintenance or translation of the computer system, it is usually **system software**.
- If the main purpose is to let the user complete a task such as writing, calculating, browsing or designing, it is usually **application software**.

Why does this matter? Because software in a computer system is layered. The hardware is at the bottom. System software sits close to the hardware and manages it. Application software sits above that and uses the services provided by system software.

For example, when a user saves a file in a word processor, the word processor is not directly controlling the disk hardware by itself. It relies on the operating system to handle storage access, memory use and input/output. So the application performs the user task, but the system software makes that possible.

> **Key Term: hardware**
> The physical components of a computer system.
>
> **Key Term: system software**
> Software intended to allow the computer system to run and support other software.
>
> **Key Term: application software**
> Software intended to allow the end user to achieve a task.

This is why you should avoid weak definitions such as “system software is software that runs in the background” or “application software is software you click on”. Those descriptions are unreliable. A utility program can be opened by the user, but it is still system software. A game may run full screen and control many resources, but it is still application software because its purpose is the user’s task.

> **Test Tip:** In classification questions, focus on the program’s main purpose, not whether the user can see it or interact with it.

### Application software: software for user tasks

Application software is designed to help the user do something useful. That “something” may be work, communication, creativity, entertainment or control of a specialist activity.

Common examples include:

- word processors
- spreadsheets
- web browsers
- database packages
- graphics editors
- games
- CAD software

The shared feature is that the software is aimed at an end-user goal. A spreadsheet helps a user model finances. A browser helps a user access web pages. A graphics editor helps a user manipulate images.

It is worth being precise here. The exam is unlikely to reward vague statements such as “application software is software people use”. A better answer explains the purpose:

- A **word processor** is application software because it helps the user create and edit documents.
- A **web browser** is application software because it helps the user access and use web resources.
- A **game** is application software because it performs a user-oriented task: entertainment.

Application software can be broad or narrow in purpose. Some programs can be used for many tasks. A word processor can write essays, letters, revision notes or reports. Others are more specific, such as flight simulator training software or audio editing software. For this subtopic, the main point is still the same: if the software’s purpose is to help the end user complete a task, it belongs in the application category.

A common mistake is to assume that software supplied with the computer must be system software. That is not true. A laptop may come with a browser, media player or photo editor pre-installed, but these are still application programs because of what they are for.

Another common mistake is to say that any software used by a programmer is system software. That is also false. A programmer may use a text editor or IDE to write code, but a **translator** is system software because it converts code for execution, whereas an editor is not automatically in that category just because a programmer uses it.

> **Key Term: application**
> A program used by an end user to perform a specific task.

To reason this through, ask two questions:

1. What job is the software trying to achieve?
2. Is that job mainly for the user, or mainly for the computer system?

If the answer is “for the user”, it is application software.

> **Test Tip:** If a question gives examples such as browser, spreadsheet or game, classify them first and then justify your answer with purpose: “used by the end user to perform a task”.

### System software: software that keeps the system usable

System software supports the operation of the computer system itself. In the AQA specification, four main categories matter:

- operating systems
- utility programs
- libraries
- translators

Students often remember the operating system but forget the other three. That loses marks, especially on “name” or “identify” questions.

#### Operating systems

The **operating system** is the main piece of system software. It sits between hardware and applications. It provides a user interface, manages resources, and gives application programs a platform to run on.

If there were no operating system, using the hardware directly would be much harder. Each application would have to manage memory, input/output and hardware control by itself. In practice, the operating system hides much of that complexity.

You do not need full operating system detail for this subtopic, but you should know why it belongs in system software:

- it manages hardware resources
- it supports the execution of applications
- it provides services to users and programs

Examples of operating system functions include memory management, interrupt handling, input/output management, multitasking, peripheral management and providing a user interface.

> **Key Term: operating system (OS)**
> System software that manages hardware and software resources and provides a platform for application software to run.

#### Utility programs

Utilities are system software designed to maintain, protect, configure or optimise the computer system. They do not usually exist to achieve the user’s main task. Instead, they help the system stay efficient, secure or organised.

Examples include:

- antivirus or virus scanning software
- backup software
- disk cleanup tools
- file management tools
- system monitoring tools
- disk defragmentation software for hard disk drives
- compression software
- encryption utilities
- firewall software

The reasoning matters. A backup utility is not classed by whether the user launches it manually. It is classed by purpose. Its purpose is system maintenance and protection, so it is system software.

Students also confuse utilities with the operating system itself. A utility is not simply “part of the OS”, even if it may be supplied with it. In classification terms, a utility is its own type of **system software**.

> **Key Term: utility program**
> System software designed to maintain, protect, configure or optimise a computer system.

#### Libraries

A **library** is a collection of pre-written code that other programs can use. This often includes functions, procedures, classes or subroutines that solve common tasks.

Examples of what a library might contain include:

- mathematical routines
- file handling routines
- graphics functions
- networking functions

Why is this system software in the AQA context? Because libraries support software development and execution rather than acting as direct end-user tools. They save programmers from rewriting common operations and improve reliability because reused routines are often already tested.

For example, if a programmer wants a program to calculate square roots or draw graphics on screen, they may call code from a library instead of writing those operations from scratch. The library supports the running or building of software; it is not the end-user task itself.

A common exam error is to describe a library as “a place where files are stored” or “documentation for programmers”. That is not the meaning here.

> **Key Term: library**
> A collection of pre-written code or routines that can be used by other programs.

### Translators: turning source code into executable form

A translator is system software that converts program code from one form into another so that it can be executed by the computer.

This is necessary because the CPU can execute **machine code**, but programmers usually write programs in **high-level language** or **assembly language**. The processor cannot directly execute most source code written by humans. It needs translation first.

> **Key Term: translator**
> System software that converts source code into machine code or another executable form.

There are three translator types you must know.

#### Compiler

A **compiler** translates the whole high-level program before execution. It usually produces object code or an executable file.

The key point is timing: translation happens first, then execution can happen later.

This has several effects:

- the program does not need to be translated every time it runs, unless the source code changes
- errors are usually reported after compilation
- the distributed version can be an executable rather than the original source code
  > **Key Term: compiler**
  > A translator that converts the whole high-level language program into machine code or object code before execution.

#### Interpreter

An **interpreter** translates and executes code line by line. Translation happens during program execution rather than fully in advance.

This means:

- execution usually stops when an error is reached
- source code is translated each time the program runs
- it does not usually produce a standalone executable in the same way as a compiler
  > **Key Term: interpreter**
  > A translator that converts and executes high-level code one line at a time.

#### Assembler

An **assembler** translates **assembly language** into machine code.

This is different from a compiler because a compiler starts with a high-level language. An assembler starts with assembly language, which is much closer to machine code and is processor-specific.

> **Key Term: assembler**
> A translator that converts assembly language into machine code.

A useful comparison is below.

| Translator  | Input               | How translation happens                        | Output                           |
| ----------- | ------------------- | ---------------------------------------------- | -------------------------------- |
| Compiler    | High-level language | Whole program translated before running        | Object code or executable        |
| Interpreter | High-level language | Line by line during execution                  | Usually no standalone executable |
| Assembler   | Assembly language   | Converts assembly instructions to machine code | Machine code                     |

Now link this back to software classification. Translators are **system software** because they support the running of programs and the operation of the system. They are not classed by who uses them, but by what they do.

Suppose a programmer writes a Python-style program. An interpreter may translate and execute it line by line. Suppose a programmer writes C-like code. A compiler may translate it into executable code. Suppose a programmer writes assembly instructions using mnemonics. An assembler converts those mnemonics into machine code. In each case, the translator exists because the CPU needs machine-readable instructions.

Students often mix these up, so make the distinctions exact:

- **compiler**: whole program first
- **interpreter**: line by line during running
- **assembler**: assembly language only
  > **Test Tip:** If asked to compare translators, always state the input language, when translation happens, and whether executable code is produced. Those are the usual mark points.

### How to classify software in exam questions

Many exam questions on this topic are really tests of careful reading. The program name alone is not enough; you need to link it to purpose.

Use this method:

1. Identify what the software mainly does.
2. Decide whether that job supports the system or helps the end user complete a task.
3. If it is system software, place it into the correct subtype.

Worked examples:

- **Microsoft Word**: application software, because it helps the user create and edit documents.
- **Google Chrome**: application software, because it helps the user access websites.
- **Antivirus tool**: utility program, therefore system software, because it protects and maintains the computer system.
- **Backup software**: utility program, therefore system software, because it preserves data and supports maintenance.
- **A collection of maths functions used by programs**: library, therefore system software.
- **A program that converts Java-like source code line by line**: interpreter, therefore system software.
- **A program that converts assembly mnemonics into binary instructions**: assembler, therefore system software.
- **Windows or Linux**: operating system, therefore system software.

Common student errors include:

- saying “the OS” when the example is actually a utility
- saying “application” because a user can open the program
- forgetting that libraries and translators are classed as system software
- confusing compiler and interpreter
- confusing assembler with compiler

To improve precision, answer using full classification language. For example, instead of writing “antivirus is software that helps the computer”, write “antivirus is a utility program, which is a type of system software used to protect and maintain the computer system”.

## Key Point Checklist

_This article has covered the following key knowledge points:_

- A computer system works through the combination of hardware and software
- Software is classified into two broad groups: system software and application software
- Application software helps the end user perform tasks such as writing documents, browsing the web or editing images
- System software supports the running and maintenance of the computer system
- The four main AQA categories of system software are operating systems, utility programs, libraries and translators
- An operating system manages hardware resources and provides a platform for applications
- Utility programs maintain, protect, configure or optimise the system
- Libraries are collections of pre-written code used by other programs
- Translators are system software because they convert source code into executable form
- A compiler translates the whole high-level program before execution
- An interpreter translates and executes high-level code line by line
- An assembler translates assembly language into machine code

## Key Terms and Concepts

- software
- hardware
- system software
- application software
- application
- operating system (OS)
- utility program
- library
- translator
- compiler
- interpreter
- assembler


Computer Systems - Software classification