Operating system

An operating system (OS) is system software that manages computer hardware and software resources, and provides common services for computer programs. It helps organize and control how computers work.

Time-sharing operating systems schedule tasks to use the system efficiently. They can also keep track of how resources like processing power and storage are used.

Operating systems are found on many devices with a computer, from phones and game consoles to powerful servers and supercomputers. As of November 2025, Android is the most popular operating system, used on many smartphones. Other common operating systems include Microsoft Windows for desktop computers, iOS and iPadOS for Apple devices, and macOS for Mac computers. Linux is widely used on servers and very powerful computers. Some operating systems are made for special jobs, like controlling machines or keeping information safe.

Definition and purpose

An operating system is like a helper for your computer. It manages the computer's resources so that everyone who uses the computer and all the programs can work together smoothly. It includes special software called a kernel that is always running, plus other helpful tools.

The operating system has three main jobs:

• It shares the computer's power and memory between different programs so that no single program can take over everything. It also keeps programs safe from each other.
• It makes using the computer's hardware easier for programmers by hiding complicated details. It can even make it seem like the computer has more memory than it really does.
• It offers common services, like ways to connect to networks or save files, so programs can run on different types of computers without needing changes.

Types of operating systems

Operating systems help manage computer hardware and software. Some operating systems are designed for use with many computers working together, like in cloud computing. These systems help computers share tasks and information efficiently.

Other operating systems are made for specific uses, like in household appliances or devices that need to complete tasks at exact times, such as in manufacturing. Some operating systems can run inside other systems, allowing different tasks to be tested or moved between computers easily.

History

Main article: History of operating systems

The earliest computers from the 1940s and 1950s needed people to set them up by hand or use special cards to tell them what to do. When transistors were invented in the 1950s, bigger computers called mainframes were made. These still needed someone to manage them, but they started to have simple operating systems to help run programs.

In the 1960s, IBM made a series of computers that all used the same operating system, OS/360. This system could handle multiple tasks at once, letting one task wait while another used the computer's brain. Around this time, ways to let many people use a computer at the same time were developed. One system, MULTICS, aimed to let hundreds of users access a big computer together. From this, the UNIX operating system grew, which led to many different versions like System V and BSD. A simpler version called MINIX inspired Linux, which is now widely used in data centers and phones.

The creation of personal computers became possible in the 1980s. For a while, CP/M was the most common operating system for these small computers. Later, IBM and Microsoft created MS-DOS, which became very popular. The first computer to use a graphical user interface, making it easier to use, was Apple's Macintosh. This idea was later added to MS-DOS by Microsoft, creating Windows. Today, Windows is still widely used on personal computers, while UNIX systems like Linux are common on business computers and servers. On mobile devices, Symbian OS was first, followed by BlackBerry OS and iOS. Eventually, the open-source Android operating system became the most popular for smartphones and other mobile devices.

Components

The parts of an operating system work together to make sure all the pieces of a computer work well together. Since older ways of doing things like DOS are no longer used, all programs need the operating system to talk to the computer's hardware.

Kernel

The kernel is a important part of the operating system. It keeps different programs and users separate to make the computer more reliable and secure. It helps keep errors in one program from affecting others and stops any one program from taking over the whole computer. The kernel works in different ways depending on whether it is handling basic tasks or more advanced ones.

Program execution

The operating system acts like a middleman between programs and the computer's hardware. It helps programs talk to the hardware by following certain rules. When a program starts, the operating system sets up space for it to work and gives it what it needs to run.

Interrupts

Interrupts are signals that tell the computer to stop what it's doing and handle something else right away. This helps the computer respond quickly to things like pressing a key or moving a mouse. There are two types of interrupts: ones that come from the computer's hardware and ones that come from programs.

Input/output

The operating system includes special programs called drivers that help the computer talk to devices like keyboards, mice, and hard drives. When you press a key or move a mouse, the computer uses interrupts to respond right away.

Memory management

The operating system keeps track of all the memory in the computer to make sure each program gets the space it needs and doesn't interfere with others. It protects memory so that one program can't accidentally mess up another program's data.

Concurrency

Modern operating systems can handle many tasks at once. They use threads, which are smaller parts of programs that can run separately. The operating system decides which threads get to run and for how long.

File system

The operating system helps you store and organize files on the computer. It uses filenames and folders to keep track of where things are. It also makes sure your files are safe even if the computer turns off suddenly.

Networking

Most operating systems include ways to connect to other computers and the internet.

Security

Operating systems protect your computer from things that might try to hurt it. They keep your information safe and make sure only the right people can see or change it.

User interface

Operating systems have ways for you to talk to the computer. You can either type commands or use a graphical interface with windows, icons, and a mouse. Most people prefer the graphical way because it's easier to use.

Operating system development as a hobby

Main article: Hobbyist operating system

Some people enjoy creating their own operating systems as a fun activity. These systems are made from scratch, without copying existing ones, and usually have only a few users and developers.

People might build these systems for simple devices, like a small computer board using a 6502 microprocessor, or for common types of computers. They can start with brand-new ideas or copy parts of existing systems. The person creating the system works alone or with a small group of friends who share the same interest.

Examples of such hobby operating systems are Syllable and TempleOS.

Diversity of operating systems and portability

When an application is made to work on one kind of operating system and then changed to work on another, it might need to be adjusted because each operating system does things a little differently. This can take time and effort.

To avoid this problem, some applications are built using special tools like Java or Qt. These tools help the application work on many different operating systems without needing many changes. Another way to make things easier is for operating system makers to follow common rules, such as POSIX, which helps applications run better on different systems.

Popular operating systems

Further information: Usage share of operating systems and Comparison of operating systems

As of October 2025, Android, based on the Linux kernel, is the most popular operating system with a 38% market share, followed by Microsoft Windows at 31%, iOS and iPadOS at 15%, macOS at 7%, and Linux at 1%. Android, iOS, and iPadOS are mobile operating systems, while Windows, macOS, and Linux are desktop operating systems.

Linux

Main article: Linux

Linux is free software that anyone can use and change. It was made by programmers for themselves, so it is simple and consistent. Linux can run on very small computers or very large ones. It has a graphical user interface that you can use with a mouse, or you can type commands to tell the computer what to do.

Android is an operating system based on Linux that is used on many smartphones and other devices like smart watches, automotive dashboards, and home appliances.

Microsoft Windows

Main article: Microsoft Windows

Windows is an operating system used on many types of computers and devices, including desktop computers, laptops, tablets, and Xbox consoles. It was designed to be secure, reliable, and able to work with many different types of hardware. Windows includes features to help protect your information and manage how programs run on your computer.