What is an operating system? In short, it is the software that manages a computer’s hardware and lets other programs run. Without an operating system (OS), every application would need its own code to control the processor, memory, disk, screen and network. The OS does that work once, safely, for everyone.
This guide explains what an OS does, how it starts, its main parts and the most common examples today.
What an operating system does
An operating system has three big jobs:
- Manage resources: share the CPU, memory, storage and devices between programs.
- Provide services: give applications a simple way to read files, use the network or draw on the screen.
- Protect the system: keep programs and users from interfering with each other.
For a detailed list, see functions of the operating system.
Main parts of an OS
| Part | Role |
|---|---|
| Kernel | Core of the OS; runs in privileged mode and controls hardware |
| Device drivers | Let the kernel talk to specific hardware |
| System libraries | Give programs standard functions, such as file and network access |
| System services | Background programs, such as logging, networking and updates |
| User interface | Command line (shell) or graphical desktop |
Programs run in user space and ask the kernel for help through system calls. This separation keeps a crashing app from bringing down the whole computer.
How a computer starts (booting)
- The firmware (UEFI or BIOS) tests the hardware.
- Next, it loads a bootloader, such as GRUB or Windows Boot Manager.
- The bootloader loads the kernel into memory.
- Then the kernel initialises drivers and starts the first process, such as systemd on Linux.
- Finally, system services start, and you see a login screen.
Secure Boot checks that each step is signed, which blocks some types of malware.
Popular operating systems
| OS | Typical use | Notes |
|---|---|---|
| Windows | Desktops, laptops, many business servers | Largest desktop market share |
| macOS | Apple computers | Unix-based, certified UNIX |
| Linux | Servers, cloud, embedded devices, some desktops | Free and open source; many distributions |
| Android | Smartphones, tablets, TVs | Based on the Linux kernel |
| iOS and iPadOS | iPhones and iPads | Closely tied to Apple hardware |
| ChromeOS | Chromebooks | Browser-centred, Linux underneath |
Most of the internet runs on Linux, while most office desktops run Windows. Read more about the differences in Linux vs Windows.
Free vs paid operating systems
You can get capable operating systems for free. Linux distributions such as Ubuntu, Debian and Fedora cost nothing, and ChromeOS Flex can revive older PCs. Windows and macOS licences are usually included with new hardware, while Windows Server and enterprise Linux subscriptions cost extra for support.
Choosing an operating system
- Office and general use: Windows or macOS.
- Servers and cloud: Linux, unless you need Microsoft-specific services.
- Learning IT and security: Linux, often in a virtual machine.
- Old hardware: a lightweight Linux distribution.
- Development: any of the three; many developers use Linux tools, even on Windows through WSL.
Related guides
Sources
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