Operating System
Summary: System software that manages computer hardware, runs applications, provides a user interface, handles file management, and manages memory and processes. Acts as an intermediary between hardware and application software. Examples: Windows, macOS, Linux, Android, iOS. Tags: igcse computer-science Created: 2026-05-08T14:03:00Z Last Updated: 2026-07-16
What is an Operating System?
An operating system (OS) is the most fundamental piece of software on a computer. It manages all hardware resources (CPU, memory, storage, input/output devices), provides a platform for application software to run, and offers a user interface. Without an OS, each application would have to include its own code for every type of hardware and every basic function — a practical impossibility.
The OS acts as a layer of abstraction between hardware and applications: programs interact with the OS using standardised interfaces, and the OS translates those requests into hardware-specific commands via device drivers.
Functions of an Operating System
1. Provide a User Interface
The OS provides a way for users to interact with the computer:
| Interface | Description | Example |
|---|---|---|
| GUI (Graphical User Interface) | Visual interface with windows, icons, menus, pointer (WIMP). Designed for ease of use. | Windows desktop, macOS Finder, GNOME on Linux |
| CLI (Command Line Interface) | Text-based interface where users type commands. More powerful for automation and scripting. | Windows Command Prompt, bash on Linux/macOS |
Most modern operating systems provide both. The CLI is preferred by developers and system administrators for its scriptability and efficiency.
2. Manage Hardware and Peripherals (Device Drivers)
The OS uses device drivers — specialised programs that translate OS commands into the specific instructions a hardware device understands. Each piece of hardware (printer, graphics card, keyboard, network adapter) requires a driver.
- The OS provides a standard interface for applications (e.g., “print this document”)
- The driver translates that request for the specific printer model
- This means applications do not need to know how every printer works
3. Manage Memory
The OS allocates RAM to programs and ensures they do not interfere with each other:
- Each program gets its own address space — it cannot access memory allocated to other programs
- The OS tracks which parts of RAM are free and which are in use
- Virtual memory: when RAM is full, less-used pages are moved to disk (see RAM for virtual memory and thrashing)
- Memory is reclaimed when a program closes
4. Manage Processes
A process is a program in execution. Modern operating systems run many processes simultaneously.
- Multitasking: The OS rapidly switches between processes, giving each a small time slice on the CPU. This creates the illusion of simultaneous execution on a single-core CPU.
- Scheduling: The OS decides which process runs next based on priority, fairness, and resource needs
- Interrupt handling: Hardware and software interrupts allow the OS to respond to events (keyboard presses, timer ticks, I/O completion)
- Process isolation: A crash in one process does not affect others (the OS terminates only the misbehaving process)
See Interrupt for more on how interrupts work.
5. Manage Files
The OS provides a structured way to store and retrieve data:
- Creates, reads, writes, renames, copies, and deletes files
- Organises files into a hierarchical directory structure (folders/directories)
- Manages metadata: file name, size, type, creation/modification dates, permissions
- Controls access: read, write, and execute permissions for users and groups
- Manages free space on storage devices
6. Manage Security
The OS enforces security through:
- User accounts: Each user has a unique identity with a password or other authentication
- Access control: Users have different privilege levels (administrator vs standard user)
- Authentication: Verifying a user’s identity at login
- Firewall integration: Controlling network traffic
- Encryption: Protecting stored data (e.g., BitLocker on Windows, FileVault on macOS)
7. Provide a Platform for Applications
The OS provides APIs (Application Programming Interfaces) that applications use to access system services — opening files, drawing windows, playing sounds, connecting to networks. This means application developers do not need to write low-level hardware access code.
Examples of Operating Systems
| OS | Type | Primary Use |
|---|---|---|
| Microsoft Windows | Proprietary | Desktop PCs, laptops, business environments |
| macOS | Proprietary (Unix-based) | Apple Mac desktops and laptops |
| Linux (Ubuntu, Fedora, Debian, etc.) | Open source (Unix-like) | Servers, developers, Android is Linux-based |
| Android | Open source (Linux kernel) | Smartphones, tablets |
| iOS | Proprietary | iPhones, iPads |
| Chrome OS | Proprietary (Linux kernel) | Chromebooks (web-focused) |
Sources
- BBC Bitesize GCSE Computer Science — Operating Systems, BBC (free educational resource)
- Cambridge IGCSE Computer Science 0478 — Software, Cambridge Assessment International Education
- CK-12 Computer Science — System Software, CK-12 Foundation (free, CC BY-NC 3.0)
Related Notes
- System Software — OS is the core of system software
- Application Software — Programs that run on top of the OS
- Interrupt — How the OS responds to hardware/software events
- RAM — Memory the OS manages and allocates
- Virtual Memory — The OS’s disk-based RAM extension
- File Handling — How programs interact with the OS file system
- Firmware — Low-level software between OS and hardware
- CS-Index
Common Misconceptions
| Misconception | Reality |
|---|---|
| ”The OS is the same as the GUI” | The GUI is just one component of the OS. The OS kernel, memory manager, process scheduler, and device drivers operate with or without a GUI. |
| ”Linux is an operating system” | Linux is technically a kernel. A full OS (like Ubuntu or Fedora) is the Linux kernel plus GNU utilities and other software — hence “GNU/Linux”. |
| ”The OS runs on top of applications” | Applications run on top of the OS. The OS is the foundation, directly controlling the hardware. |
| ”More RAM means the OS does less memory management” | The OS always manages memory regardless of how much is available. More RAM reduces the need for virtual memory but does not eliminate memory management. |
| ”Closing a window always stops the program” | On many systems, closing the window does not necessarily terminate the process — some programs continue running in the background. |