Definition
An operating system (OS) is the foundational software that runs on a computer and acts as an intermediary between the user, the applications they run, and the underlying hardware. Without an operating system, application software would need to communicate directly with the CPU, memory, and storage — an impossibly complex task for every developer to handle independently.
The OS handles these low-level details so that applications can focus on their specific purpose.
Main Functions of an Operating System
Process Management
The OS controls which programs run, when they run, and how much CPU time each receives. On a modern computer, many processes (running programs) exist simultaneously — the OS schedules them, giving each a brief turn on the CPU so quickly that it appears everything is running at the same time.
Memory Management
The OS allocates portions of RAM to each running program and ensures that programs cannot interfere with each other's memory. When a program closes, the OS reclaims that memory for future use.
File System
The OS provides a structured way to store, organise, retrieve, and delete data on storage devices. It manages directories (folders), file names, permissions, and the physical location of data on disk.
User Interface
The OS provides the means by which users interact with the computer — either through a Graphical User Interface (GUI) with windows, icons, and menus, or through a Command Line Interface (CLI) where the user types text commands.
Even when you think no programs are open, the OS itself is always running in the background — managing hardware drivers, handling network connections, processing system events, and much more.
Examples of Operating Systems
| Operating System | Primary Use |
|---|---|
| Windows | Personal computers and laptops (Microsoft) |
| macOS | Apple Mac computers |
| Linux | Servers, developer workstations, and embedded systems |
| Android | Smartphones and tablets (based on Linux) |
| iOS | Apple iPhones and iPads |
| ChromeOS | Chromebook laptops (Google) |
Linux is not a single operating system but a family of distributions (distros) — Ubuntu, Fedora, Debian, and many others — all built around the same core (the Linux kernel). Most of the world's web servers run Linux.
The OS as an Abstraction Layer
One of the most important concepts behind an operating system is abstraction: hiding complexity behind a simple interface. A program that wants to read a file does not need to know whether the data is stored on an HDD, an SSD, or a network drive — it simply asks the OS, and the OS handles the details.
This is why the same application (such as a web browser) can run on many different hardware configurations without being rewritten for each one.
Practice Problems
Name four main functions of an operating system.
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What is the difference between a GUI and a CLI?
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Why does every program need an operating system?