Operating system
The layer of software that manages a computer's resources for its users and their applications.
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An operating system (OS) is system software that manages computer hardware and software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient system use and may include accounting software to allocate costs for processor time, storage, and peripherals. For hardware functions like input/output and memory allocation, the OS acts as an intermediary between programs and hardware, though application code usually executes directly on the hardware and frequently makes system calls to the OS or is interrupted by it. Operating systems are found on many devices containing a computer, from phones and game consoles to web servers and supercomputers.
Popular operating systems
Android holds a 38% market share, followed by Microsoft Windows at 33%, iOS and iPadOS at 15%, macOS at 4%, and Linux at 1%. Android, iOS, and iPadOS are for mobile devices; Windows, macOS, and Linux are for desktops. Linux distributions dominate servers and supercomputers and number in the thousands.
Specialized classes include embedded and real-time systems, as well as security-focused operating systems. Some have low system requirements, like lightweight Linux distributions, while others require more. Operating systems may require installation, come pre-installed on computers, or run directly from media like a live CD or USB stick.
The OS includes a kernel—software always running—along with system programs (associated but not part of the kernel) and applications. Its three main purposes are allocating resources (CPU time, memory) between applications while isolating them for protection; providing an abstraction layer for hardware access, including virtualization like virtual memory; and offering common services such as network and disk interfaces, enabling applications to run on different hardware without rewriting. Multiprocessor systems share memory across CPUs, while multicomputers (common in cloud computing) have CPUs with their own memory, requiring message passing, multiqueue designs, or remote direct memory access for performance. Distributed systems consist of networked computers with their own OS and file systems, often using middleware for consistency.
Quick Facts
- Field
- System software
Facts from the source article.
Lore & Background
The first computers in the late 1940s and 1950s were directly programmed either with plugboards or with machine code inputted on media such as punch cards, without programming languages or operating systems. After the introduction of the transistor in the mid-1950s, mainframes began to be built.
These still needed professional operators who manually do what a modern operating system would do, such as scheduling programs to run, but mainframes still had rudimentary operating systems such as Fortran Monitor System (FMS) and IBSYS. In the 1960s, IBM introduced the first series of intercompatible computers (System/360). All of them ran the same operating system—OS/360.
Reader's Guide
Operating systems manage hardware and software resources, scheduling tasks for efficient use and often including accounting software for cost allocation of processor time, storage, and peripherals. They act as intermediaries for hardware functions like input/output and memory allocation, though application code typically runs directly on hardware, making system calls or being interrupted by the OS. Found in devices from smartphones and game consoles to web servers and supercomputers, operating systems vary widely in market share: Android leads at 38%, followed by Windows at 33%, iOS/iPadOS at 15%, macOS at 4%, and Linux at 1%.
Mobile OSes include Android, iOS, and iPadOS; desktop OSes include Windows, macOS, and Linux, with Linux dominating servers and supercomputers. Specialized types exist, such as embedded and real-time systems, security-focused OSes, and lightweight distributions with low system requirements. Some OSes require installation or come pre-installed, while others run directly from live media or USB sticks. The kernel is the always-running core, but system programs and applications also run.
Operating systems allocate resources like CPU time and memory, isolate applications to prevent monopolization and protect against errors, and provide hardware abstraction via virtualization, such as virtual memory. They offer common services for network and disk access, enabling application portability across hardware. Types include multicomputer OSes for clusters with multiple CPUs each having its own memory, distributed systems with networked computers often using middleware, embedded OSes for devices like smart cards that do not load user software, and real-time OSes that guarantee event processing by specific times.
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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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Operating system (CC BY-SA 4.0).
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