An operating system is the software that runs your computer and lets you use it
An operating system (OS) is the main program that controls everything your computer does. It manages your hardware — the keyboard, mouse, screen, hard drive, and processor — and lets you run other programs like web browsers, email clients, and word processors. Without an operating system, your computer is just a box of parts that cannot talk to each other.
Think of it this way: the operating system is the translator between you and your machine. When you click an icon, the OS tells the processor what to do. When you save a file, the OS tells the hard drive where to put it. When you plug in a printer, the OS recognizes it and makes it work with your other programs.
Your computer cannot start without an operating system. When you turn on your machine, the first thing that loads is the OS. It stays running the entire time you use the computer, managing every task in the background.
Key Takeaways
- The three most common operating systems for personal computers are Windows (made by Microsoft), macOS (made by Apple), and Linux (free and open-source).
- An operating system manages your hardware, runs your programs, and handles files and folders on your hard drive.
- Windows runs on most PCs worldwide and is the easiest to find software for, but macOS and Linux are alternatives with different strengths.
- Mobile devices like phones and tablets use their own operating systems — Android and iOS — which work differently from computer operating systems.
- You cannot change your operating system without erasing your computer or buying a new one, so choosing the right one matters when you buy.
Windows: The most widely used operating system
Windows, made by Microsoft, runs on roughly 75 percent of personal computers worldwide. It comes pre-installed on most PCs you buy from manufacturers like Dell, HP, Lenovo, and Asus. Windows is familiar to most people because it has been the standard in offices, schools, and homes for decades.
The current version is Windows 11, released in 2021. Older computers may still run Windows 10, which Microsoft still supports. Windows is known for having the largest library of software available — if you need a program for something specific, it probably exists for Windows first.
Windows is also the easiest operating system to repair and upgrade yourself. Hard drives, memory, and other parts are inexpensive and widely available. If something breaks, you have many repair shops to choose from.
macOS: The operating system built into Apple computers
macOS runs only on Apple computers — the MacBook, iMac, and Mac Mini. You cannot install macOS on a regular PC. Apple designs both the hardware and the operating system together, which means macOS is optimized specifically for Apple machines.
macOS is known for being stable and rarely crashes. It also has strong built-in security features. Many creative professionals — video editors, graphic designers, and musicians — prefer macOS because certain professional software runs better on it.
The downside is cost. Apple computers are significantly more expensive than Windows PCs with similar power. Repairs are also more expensive because only Apple stores and certified technicians can work on them. If you need very specific software, it may not exist for macOS.
Linux: The free and open-source alternative
Linux is free software that anyone can read and install. It is open-source, meaning the code is publicly available and anyone can modify it. Linux runs on millions of servers worldwide and powers much of the internet behind the scenes.
For personal computers, Linux is less common than Windows or macOS. Popular versions for regular users include Ubuntu, Fedora, and Linux Mint. Linux is powerful and flexible, but it requires more technical knowledge to use and troubleshoot than Windows or macOS.
Linux is a good choice if you are comfortable with computers, want to save money, or need a system you can customize heavily. It is not a good choice if you need specific software that only runs on Windows or macOS, or if you want a system that works the same way as what you already know.
What an operating system actually does every day
Your operating system handles dozens of tasks at once without you thinking about it. It manages memory — deciding which programs get how much RAM so nothing crashes. It handles your file system — organizing your documents, photos, and programs into folders so you can find them. It controls permissions — deciding what you can and cannot do with each file.
The OS also manages your internet connection, handles printing, controls your screen brightness and volume, and runs security scans in the background. It updates itself with security patches to fix vulnerabilities that hackers could exploit. Every time you open a program, the OS loads it into memory and gives it resources to run.
You interact with the OS through the user interface — the desktop, icons, menus, and windows you see on your screen. Different operating systems organize this interface differently, which is why switching from Windows to macOS feels unfamiliar at first.
Operating systems on phones and tablets are different
Phones and tablets use operating systems designed for touch screens and mobile devices. The two main ones are Android (used by Samsung, Google Pixel, and most other phones) and iOS (used only by iPhones and iPads).
Mobile operating systems work differently from computer operating systems. They use less power, manage battery life carefully, and are designed around apps rather than programs. You cannot install a Windows or macOS program on a phone, and you cannot run Android or iOS on a regular computer.
If you use both a computer and a phone, they may have different operating systems. Many people use Windows on their computer and Android on their phone, or macOS on their computer and iOS on their phone. They do not need to match.
How to find out which operating system you have
On Windows: Click the Start button (bottom left), type "About your PC" into the search box, and click the result. You will see your Windows version and edition.
On macOS: Click the Apple menu (top left), select "About This Mac", and you will see your macOS version.
On Linux: Open a terminal and type uname -a or lsb_release -a depending on your distribution. The output will show your Linux version.
You can also usually see your operating system name on the login screen when you first turn on your computer, or in the system settings.
Choosing an operating system when you buy a computer
When you buy a new computer, the operating system comes pre-installed. You choose the OS by choosing the brand and model. If you buy a Dell or HP, you get Windows. If you buy a MacBook, you get macOS. If you want Linux, you either buy a computer with it pre-installed (rare) or install it yourself after purchase (requires technical skill).
Switching operating systems later is not practical for most people. You would need to erase your entire hard drive and start over, losing all your files and programs. Some people run two operating systems on one computer using virtualization software, but this is slower and requires more technical knowledge.
The best time to think about which operating system you want is before you buy. Consider what software you need, what you are comfortable using, and what your budget allows. If you are unsure, Windows is the safest choice because it is familiar to most people and has the most software available.
Frequently Asked Questions
Can I install Windows on a Mac or macOS on a Windows computer?
You cannot install macOS on a Windows PC — Apple does not allow it. You can install Windows on some newer Macs using special software, but it is complicated and not recommended for regular users. It is simpler and cheaper to buy the computer with the operating system you want.
What happens if I do not update my operating system?
Operating system updates include security patches that fix vulnerabilities hackers can exploit. If you do not update, your computer becomes less find over time. Updates also fix bugs and add new features. Most updates happen automatically, but you should restart your computer when prompted to complete them.
Is Linux safe to use?
Linux is very find and is used on most servers that handle sensitive data. However, security also depends on how you use it. Any operating system — Windows, macOS, or Linux — can be compromised if you read malware or use weak passwords. Linux is safe if you know what you are doing, but it requires more caution than Windows or macOS.
Do I need to buy an operating system separately?
No. Windows and macOS come pre-installed on computers you buy, and you pay for them as part of the computer price. Linux is free to read and install yourself. You only buy an operating system separately if you want to upgrade an older computer to a newer version, which is rare.
Can two people use the same computer with different operating systems?
No. A computer runs one operating system at a time. Multiple people can use the same computer by logging in with different user accounts, but they all use the same operating system. Each account can have different settings and files, but the OS underneath is the same.