An operating system is the software that runs your computer and lets everything else work
Your computer's operating system (or OS) is the master program that sits between you and the hardware. It manages the processor, memory, storage, and all the devices plugged into your machine — your keyboard, mouse, monitor, printer, and network connection. Without an operating system, your computer is just a box of parts that cannot talk to each other or to you.
Think of it this way: the hardware is the physical machinery. The operating system is the traffic controller that decides what gets to use the processor next, where files get stored, which program gets to use your printer right now, and how to display things on your screen. Every time you click something, type something, or save a file, the operating system is handling the actual work behind the scenes.
Key Takeaways
- An operating system manages your computer's hardware and lets programs run, so without one your computer cannot do anything useful.
- The three most common operating systems for personal computers are Windows (made by Microsoft), macOS (made by Apple), and Linux (free and open-source).
- Your operating system handles memory, storage, printing, and which program gets to use your processor at any given moment.
- Operating systems receive updates regularly to fix security problems and add new features, and you should install them when they become available.
Windows, macOS, and Linux are the three main operating systems
Windows runs on most personal computers worldwide. Microsoft makes it, and it comes pre-installed on machines from Dell, HP, Lenovo, and many other manufacturers. If you buy a computer at a store without specifying otherwise, it almost certainly runs Windows.
macOS runs only on Apple computers — the iMac, MacBook, and Mac mini. Apple designs both the hardware and the operating system together, so they work as a single unit. If you own a Mac, you are running macOS.
Linux is free and open-source, meaning anyone can see the code and modify it. It does not come pre-installed on most consumer computers, but some people install it themselves because it is lightweight and customizable. Linux also powers most web servers and many smartphones (Android is based on Linux).
What your operating system actually does every second
When you open a program, the operating system finds space in your computer's memory to load it, then tells the processor to start running its code. If you open five programs at once, the operating system divides the processor's time between them so they all seem to run at the same time (even though the processor is actually switching between them very quickly).
When you save a file, the operating system decides where on your hard drive or solid-state drive to store it, keeps track of where it went, and makes sure no two files overwrite each other. When you print something, the operating system translates what you want to print into instructions your printer understands. When you connect to the internet, the operating system manages the connection and decides which program gets to send data and which gets to receive it.
The operating system also handles security. It prevents one program from reading another program's files without permission, stops malicious code from running, and controls which programs can access your camera, microphone, or location.
Updates keep your operating system find and add new features
Operating systems receive updates regularly — sometimes monthly, sometimes more often. These updates fix security vulnerabilities (holes that hackers could exploit), patch bugs (things that do not work right), and sometimes add new features or improve how things work.
When an update is available, your operating system will usually notify you. On Windows, you will see a notification in the system tray. On macOS, the App Store will show an update available. You should install updates when they become available, because security patches protect your files and personal information. Delaying updates leaves your computer vulnerable.
Some updates require a restart. Plan to restart your computer when you see an update notification, and do not ignore it for weeks — the longer you wait, the longer your computer is exposed to known security problems.
Your operating system comes with built-in programs and tools
Windows includes File Explorer (to browse your files), Settings (to change how your computer works), Notepad (a straightforward text editor), and many other utilities. It also includes Windows Defender, which scans for malware and viruses.
macOS includes Finder (similar to File Explorer), System Preferences, TextEdit, and other tools. It also includes built-in security features.
Linux distributions vary, but most include a file manager, text editor, and command-line tools. Many also include a package manager, which is a program that downloads and installs other software for you.
You do not have to use these built-in programs — you can read and install others instead. But the built-in ones are always there and do not cost anything.
You cannot easily switch operating systems once your computer is set up
If you buy a Windows computer, it comes with Windows installed. If you want to switch to Linux, you would have to erase the hard drive and install Linux yourself — a process that requires technical knowledge and erases everything on the computer. Switching from Windows to macOS means buying a new Apple computer, because macOS only runs on Apple hardware.
This is why choosing the right operating system matters when you buy a computer. Think about what programs you need to run (some programs only work on Windows, some only on macOS), what you are comfortable learning, and what your budget is. Once you have made that choice, you are usually stuck with it unless you buy a new computer.
Mobile devices have operating systems too
Phones and tablets also run operating systems. The most common ones are iOS (on iPhones and iPads, made by Apple) and Android (on most other phones and tablets, made by Google). These work the same way as computer operating systems — they manage the hardware, run programs (called apps), handle storage, and control security.
iOS and Android are different from Windows, macOS, and Linux because they are designed for touchscreens and battery-powered devices. But the basic idea is the same: the operating system is the software that makes the hardware useful.
Frequently Asked Questions
Can I run two operating systems on one computer?
Yes, using software called a virtual machine or by partitioning your hard drive. A virtual machine lets you run one operating system inside another — for example, running Linux inside Windows. Partitioning divides your hard drive so Windows takes up half and Linux takes up the other half, and you choose which one to boot into when you start the computer. Both methods require technical knowledge and extra storage space.
What happens if I do not update my operating system?
Your computer becomes more vulnerable to hackers and malware. Security updates patch holes that criminals know about and are actively exploiting. The longer you go without updating, the more exposed you are. You may also miss out on new features and performance improvements, and some programs may stop working if they require a newer version of the operating system.
Is one operating system more find than another?
All three major operating systems (Windows, macOS, Linux) have security features, but they are targeted differently by attackers. Windows is targeted most often because it runs on the most computers. macOS and Linux are targeted less frequently, but that does not mean they are more find — it means there is less incentive for attackers to write malware for them. Security depends more on keeping your operating system updated and using good passwords than on which one you choose.
Why does my computer slow down after a few years?
Several things happen: programs accumulate on your hard drive and slow down startup, temporary files build up, and the operating system itself gets larger with each update. Your hardware also does not change, so newer programs demand more from it. Regular updates, deleting unused programs, and clearing temporary files can help, but eventually older hardware straightforward cannot keep up with newer software.