Operating system
System software managing computer resources and providing program services.
An operating system, or OS, is the core software that oversees a computer’s hardware and software resources, offering standard services to other programs. It acts as a go-between for applications and the machine’s hardware—handling tasks like input/output and memory allocation—though application code usually runs directly on the hardware, making system calls or receiving interrupts from the OS. These systems are built into countless devices, from smartphones and game consoles to web servers and supercomputers. Time-sharing versions schedule tasks to use the system efficiently and can include accounting tools to track costs for processor time, storage, and peripherals.
The OS is notoriously tricky to pin down, but it’s often described as the software layer that manages a computer’s resources for its users and their apps. It includes the kernel, which always runs, plus other system programs that may not be part of the kernel. Applications make up the rest. An OS serves three main purposes: it allocates resources like CPU time and memory among running programs, preventing any single one from hogging the hardware; it isolates applications from each other to guard against errors and security flaws, while still allowing them to communicate; and it provides an interface that hides hardware details—like physical memory—making programming easier. Virtualization, such as virtual memory, can even give a program the illusion of nearly unlimited memory. Common services, like access to networks and disk drives, let software run on different hardware without rewriting. What services are included varies widely, and this code makes up the bulk of most operating systems.
As of late 2025, Android leads the market with a 38% share, followed by Microsoft Windows at 33%, iOS and iPadOS at 15%, macOS at 4%, and Linux at 1%. Android, iOS, and iPadOS run on mobile devices; Windows, macOS, and Linux are for desktops. Linux distributions dominate servers and supercomputers, numbering in the thousands. Specialized operating systems exist for embedded and real-time applications, along with security-focused ones. Some have low system requirements, like lightweight Linux distributions, while others demand more. Installation varies: some OSes require setup or come pre-installed on new computers, while others boot directly from a live CD or USB stick.
Multicomputer operating systems handle clusters where each CPU has its own memory, common in cloud computing due to the difficulty and cost of large multiprocessors. These systems minimize packet copying between CPUs, often using multiqueue setups or remote direct memory access, and support remote procedure calls or distributed shared memory. Distributed systems, by contrast, are groups of networked computers spread across the globe, each with its own OS and file system; middleware often sits between the OS and applications to improve consistency, though it’s not a true operating system. Embedded operating systems run on devices like household appliances, don’t load user-installed software, and thus need no application isolation, allowing simpler designs—some fit in under 10 kilobytes, with the smallest for smart cards. Examples include Embedded Linux, QNX, VxWorks, RIOT, and TinyOS. Real-time operating systems guarantee processing events within strict time constraints.
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- System software
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- Managing computer hardware and software resources, providing common services for programs, and acting as an intermediary between programs and hardware
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- Market share data for November 2025 is not yet available; statistics are typically published after the fact by analytics firms.
- other_major_operating_systems
- Market share breakdown for November 2025 is not yet available; common major operating systems include Android, Microsoft Windows, iOS/iPadOS, macOS, and Linux, but specific figures for that month are
Lore & Background
An operating system (OS) is system software that manages a computer's hardware and software resources while providing common services for computer programs. It acts as an intermediary between programs and the computer hardware for functions like input/output and memory allocation, though application code usually executes directly on the hardware and makes system calls to the OS or is interrupted by it. Time-sharing operating systems schedule tasks for efficient system use and may include accounting software to allocate costs for processor time, storage, and peripherals. Operating systems are found on devices ranging from cellular phones and video game consoles to web servers and supercomputers. The most popular OS by market share is Android at 38%, followed by Microsoft Windows at 33%, iOS and iPadOS at 15%, macOS at 4%, and Linux at 1%. Android, iOS, and iPadOS are designed for mobile devices, while Windows, macOS, and Linux are for desktops. Linux distributions dominate servers and supercomputers, numbering in the thousands. Specialized classes include embedded and real-time operating systems, as well as security-focused ones. Some OSes have low system requirements, while others require more. They may come pre-installed on computers, require installation, or run directly from media like a live CD or USB stick. The operating system includes a kernel—the software always running—along with system programs and applications. Its purposes include allocating resources like CPU time and memory among applications, isolating applications from each other while enabling communication, providing an interface that abstracts hardware details (e.g., virtual memory), and offering common services for accessing network and disk devices.
Reader's Guide
Operating systems are fundamental to modern computing, serving as the layer of software that manages a computer's resources for its users and their applications. They allocate resources between different applications, deciding when they will receive CPU time or space in memory, and isolate applications from each other to protect them from errors and security vulnerabilities. Operating systems provide an interface that abstracts hardware details, making things easier for programmers, and offer common services such as access to network and disk devices, enabling applications to run on different hardware without being rewritten. Specialized classes exist, including embedded and real-time systems, security-focused operating systems, and those with low or high system requirements. As of November 2025, Android is the most popular operating system with a 38% market share, followed by Microsoft Windows at 33%, iOS and iPadOS at 15%, macOS at 4%, and Linux at 1%. Linux distributions are dominant in the server and supercomputing sectors.
Did You Know?
- Time-sharing operating systems schedule tasks for efficient use of the system and may include accounting software for cost allocation of processor time, mass storage, peripherals, and other resources.
- For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware, although application code is usually executed directly by th
- Some operating systems require installation or may come pre-installed with purchased computers (OEM-installation), whereas others may run directly from media (i.e. live CD) or flash memory (i.e. a LiveUSB from a USB stic
- A hypervisor is not an operating system; it is a virtualization layer that runs virtual machines.
From Camera Prototypes to a Mobile Empire
Android Inc. Rubin, who had previously created the T-Mobile Sidekick at Danger Inc., initially aimed to build an operating system for digital cameras under a project called FotoFrame. The name "Android" stuck simply because Rubin already owned the android.com domain. After constructing an internal prototype called the "Fadden demo" using a custom JavaScript front-end, the startup failed to attract investors. Perlman declined any equity stake, saying he simply believed in the project.
The Open-Core Paradox
At its foundation, Android rests on the Android Open Source Project, a free and open-source codebase primarily licensed under the Apache License, originally designed for smartphones. Yet the vast majority of consumer devices do not run this pure open-source version. Instead, they ship with Google's proprietary open-core build, which layers closed-source software atop the AOSP foundation. Most prominently, this includes Google Mobile Services—a bundle containing Chrome, the Google Play digital distribution platform, and the Play Services development framework. Firebase Cloud Messaging, used for push notifications, is also recommended for developers. A critical distinction exists between the code and the brand: while AOSP remains freely available, the "Android" name and logo are registered trademarks of Google, which restricts their use on uncertified products. This creates a layered ecosystem where vendor-customized interfaces like Samsung's One UI coexist alongside community-developed alternatives such as LineageOS and Amazon's Fire OS. The source code has also been adapted for televisions, wearables, in-car systems, virtual reality headsets, and even PCs and micro consoles, demonstrating how a single codebase can span an extraordinary range of hardware form factors.
Unprecedented Global Reach
It has been the most-used smartphone operating system worldwide since 2011, and its installed base remains the largest of any operating system in existence. Software on Android is packaged in the APK format and typically distributed through a proprietary application store, though the ecosystem also accommodates a wide array of alternative channels. Beyond Google's own Play Store, users can access apps through vendor-specific platforms like the Samsung Galaxy Store and Huawei AppGallery, as well as third-party services including Aptoide, Cafe Bazaar, GetJar, and the open-source F-Droid repository. Amazon maintains its own Appstore for Fire OS devices. This multi-channel distribution model, combined with the sheer scale of the user base, has made Android a dominant force in consumer technology, with over three billion monthly active users relying on it daily.
Forging Alliances and Surviving the iPhone Shock
The group's stated mission was to develop what it called "the first truly open and comprehensive platform for mobile devices." Within a year, the alliance faced two rival open-source initiatives: the Symbian Foundation and the LiMo Foundation, the latter also pursuing a Linux-based mobile OS. The project's early prototype bore a striking resemblance to a BlackBerry, featuring a physical QWERTY keyboard and no touchscreen.
Frequently Asked Questions
What is an operating system?
An operating system is a layer of system software that sits between your applications and the physical hardware, coordinating how resources like the CPU, memory, and storage get allocated. Think of it as the traffic controller that keeps every program running smoothly without stepping on each other's toes.
What exactly does an OS do for me?
It schedules and prioritizes tasks so the processor isn't overwhelmed, manages shared resources like disk space and peripherals, and exposes common services that let programs function without each one reinventing the wheel. Some also track resource usage for cost-allocation purposes.
Which devices actually run an operating system?
Pretty much anything with a processor—from smartphones and game consoles to enterprise web servers and supercomputers—relies on an OS to make its hardware usable. The specific OS varies wildly depending on the device class and its intended workload.
What are the major operating systems people use today?
The most widely recognized names include Android, Microsoft Windows, iOS/iPadOS, macOS, and Linux, each dominating different device categories. Exact market-share percentages shift month to month and are typically reported by analytics firms after the fact.
Why can't I just run programs directly on hardware?
Without an OS, every application would need to speak raw machine-level commands to the CPU, manage memory allocation, and handle I/O on its own—making development a nightmare and multitasking nearly impossible. The OS abstracts all that complexity so developers can focus on their actual logic.
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