Describe the role and basic functions of an operating system

Operating System – Role and Basic Functions

Objective

To describe the role of an operating system (OS) and explain its basic functions as required by the Cambridge IGCSE 0478 syllabus (section 4.1).

1. Where the OS fits in the computer system

The software in a computer can be visualised as a stack of layers:

• Hardware – CPU, RAM, storage, input‑output devices.
• Firmware – Permanent code (e.g., BIOS/UEFI) that performs the first hardware initialise.
• Boot‑loader – Small programme that loads the OS kernel from storage into RAM and starts it.
• Operating System (OS) – System software that manages the hardware and provides services to other programmes.
• Application software – User‑oriented programmes such as word processors, games, web browsers.

System software vs. application software

• System software includes the operating system and utility programmes that help run, maintain and control the computer (e.g., Windows OS, macOS, Linux kernel, disk‑defragmenter).
• Application software is written to perform specific tasks for the user (e.g., Microsoft Word, Adobe Photoshop, Minecraft).

Interrupts

An interrupt is a signal that temporarily stops the current CPU activity so the OS can deal with an event.

• Hardware interrupt – generated by external devices (keyboard key press, mouse movement, network packet arrival).
• Software interrupt – generated by programmes when they request a service from the OS (system call).

The OS saves the state of the running process, services the interrupt, then restores the process.

2. Core roles and basic functions of an operating system

The Cambridge syllabus expects the following seven functions. The wording follows the exact phrasing used in the syllabus.

1. Controls the use of CPU, memory, storage and I/O devices (resource management)
   • Decides which programme gets the next CPU slice.
   • Allocates storage space and assigns devices to programmes.
2. Creates, schedules, pauses and terminates processes (process / task management – multitasking)
   • Allows several programmes to appear to run at the same time.
   • Example: While you type a document, the OS also runs a background antivirus scan.
3. Allocates and de‑allocates main memory (memory management)
   • Provides each process with its own memory space.
   • Uses paging, segmentation or swapping to make efficient use of RAM.
   • Example: When RAM is full, inactive pages are moved to a swap area on the hard‑disk.
4. Organises data on storage media (file‑system management)
   • Uses a hierarchical directory (folder) structure.
   • Supports operations: create, delete, rename, read, write, copy.
   • Maintains file attributes and permissions (read, write, execute).
   • Example: In Windows, C:\Users\Alice\Documents\report.docx resides in a folder hierarchy and may have a “Read‑only” attribute.
5. Communicates with hardware via device drivers (device management)
   • Handles input‑output requests, buffering and error detection.
   • Example: A printer driver translates generic print commands into signals the printer understands.
6. Authenticates users and enforces permissions (security and access control)
   • Checks usernames, passwords or biometrics.
   • Controls who can read, write or execute files and who may access system resources.
   • Isolates processes so one programme cannot interfere with another.
   • Example: Only the “admin” account can install new software on a Windows PC.
7. Provides a way for users to interact with the computer (user interface)
   • Two main types: Command‑Line Interface (CLI) and Graphical User Interface (GUI).
   • Example: Typing dir in a Windows CLI lists files, whereas double‑clicking an icon in the GUI opens an application.

3. Comparison of common operating systems

4. Why the OS is important for IGCSE

• Exam questions often ask you to identify and explain the seven OS functions (e.g., “What is multitasking?”).
• Programming tasks may require file handling, process control or the use of system calls.
• Security topics such as passwords, user accounts and file permissions appear in the data protection section.
• Understanding firmware, boot‑loaders and interrupts helps you answer start‑up sequence questions.

5. Quick revision checklist

• Define “operating system” and place it in the software hierarchy (hardware → firmware → boot‑loader → OS → applications).
• Distinguish system software (OS + utilities) from application software (user programmes).
• List and briefly describe the seven core OS functions required by the syllabus.
• Explain the difference between a GUI and a CLI, giving one example of each.
• State the default file system used by Windows (NTFS) and by Linux (ext4).
• Describe how the OS achieves multitasking (process scheduling, time‑slicing).
• Give a short definition of an interrupt and differentiate hardware vs. software interrupts.

Suggested diagram (for classroom use)