What an Operating System Does

Imagine a large apartment building with one manager. Tenants cook, work and sleep in their own rooms, yet they all share the same water, power and hallways. Without a manager, one noisy or careless tenant could cut off everyone else. A computer has the same problem. Many programs want the processor, the memory and the screen at once, and someone has to share them out fairly.

That manager is the operating system, often shortened to OS. It is the main piece of software on a computer. It starts first, stays running the whole time, and sits between your programs and the physical parts. This entry explains what it does, in plain terms, and how the common systems differ.

The operating system as a go-between

Programs are written to do a specific job: edit text, play music, browse the web. Writing every program so that it also knows how to talk to every possible keyboard, screen, disk and network card would be impossible. The operating system solves this by offering a standard set of services. A program asks the OS for what it needs, and the OS deals with the hardware.

This gives three practical benefits:

• Simplicity for programmers. They ask the OS to "save this file" without caring which brand of drive is installed.
• Fairness. The OS decides which program gets the processor and for how long.
• Safety. The OS keeps programs apart, so a crash in one does not usually take down the others.

If you want a picture of the hardware being managed, read how a computer works first. It covers the processor, memory and storage that the OS looks after.

The main jobs of an operating system

Most explanations group the work of an OS into a few jobs.

Running programs and sharing the processor

A running program is called a process. At any moment dozens or hundreds of processes may exist, but a processor core can follow only one list of instructions at a time. The OS switches between processes so quickly, many times each second, that they all seem to run together. The part that chooses who goes next is the scheduler.

Managing memory

Each process needs room in RAM. The OS hands out memory, tracks who is using what, and prevents one process from reading or changing another's memory. When RAM is nearly full, the OS can move rarely used data to storage to make room, which is why a computer slows down when memory runs short.

Handling files and storage

The OS gives you files and folders instead of raw storage space. It decides where the bytes of each file live and keeps track of names, sizes and who may open what. This topic has its own entry: files, folders and file systems.

Talking to devices through drivers

A driver is a small piece of software that teaches the OS how to use one kind of device, such as a printer, a graphics card or a Wi-Fi adapter. Many drivers come with the OS. Others are installed when you plug in new hardware. If a device stops working after an update, the driver is a good first suspect.

Providing networking, security and a user interface

The OS includes the basic tools for connecting to a network, and it manages user accounts and permissions, so that your files are not open to every other user of the computer. Finally, it gives you a way to interact: a graphical interface with windows, icons and menus, or a text-based one called the command line.

The kernel and the layers around it

The core of an operating system is called the kernel. It is the part that has direct control of the hardware and that does the most sensitive work: scheduling, memory and device access. Around the kernel sit other layers, such as system services, the desktop and the apps that ship with the system.

A useful way to see it is as layers, from closest to the hardware to closest to you:

Programs on the top layers cannot touch the hardware directly. They make a request, called a system call, and the kernel decides whether to carry it out. This rule is what keeps one misbehaving app from damaging the whole machine.

A worked example: two programs and a printer

Suppose you are writing a letter in a word processor while a music player runs in the background, and you press Print.

1. The word processor asks the OS to print. It does not talk to the printer itself.
2. The OS checks that you are allowed to print and passes the job to the printer driver.
3. The driver turns the page into the exact signals this printer understands.
4. While the printer works, the scheduler keeps giving the music player short turns on the processor, so the song continues.
5. If the printer runs out of paper, the OS reports the problem. Your word processor and your music keep running.

Nobody told the programs to cooperate. The operating system arranged it.

Common operating systems

Different systems exist because different devices have different needs. The names below are examples. The ideas above apply to all of them.

• Windows is made by Microsoft and runs on a very wide range of desktop and laptop computers.
• macOS is made by Apple for its own Mac computers.
• Linux is a family of systems built around the open-source Linux kernel. It runs on servers, phones, devices in homes and much more. Different packages of it are called distributions.
• Android and iOS are the two most common systems on phones and tablets. Android uses the Linux kernel.

Knowing one system helps with the others. Files, processes, permissions and drivers appear everywhere, though menus and names differ.

Common mistakes

• Mixing up the OS with the hardware. Windows and macOS are software. You can sometimes change or reinstall the OS on the same machine.
• Thinking the browser is the OS. A browser is an application that runs on top of the operating system, even when it feels like it is the only thing you use.
• Ignoring updates. The OS is the layer that keeps everything else safe. Updates often fix security flaws, so installing them matters.
• Installing drivers from random websites. Use the OS's own update tool or the maker's official site. A fake driver can carry malware.
• Assuming "a different OS" means "a different computer". Many computers can run more than one system, though this needs care and a backup.

FAQ

Is the operating system the same as an app?

No. An app does one task for you. The operating system runs in the background and supports every app. You could say that apps use the OS, and the OS uses the hardware.

Do all computers need an operating system?

General-purpose computers do, because they run many different programs. Very simple devices, such as a basic timer, may run a single program with no OS at all.

What is the difference between Linux and Ubuntu?

Linux is the kernel and the family of systems built on it. Ubuntu is one distribution, which is a ready-to-install package that combines the kernel with other software.

Can I use a computer without a graphical interface?

Yes. Servers often run with no screen at all, and administrators control them with typed commands. The command line is a normal part of IT work.

Which operating system should a beginner learn?

Start with the one you already use. The central ideas transfer, and you can explore others later. More background is in the Computing and Networks area.