Operating system

An operating system manages the resources of a computer and provides common services to applications. Its work typically includes scheduling processes to use the processor, allocating and protecting memory, organizing data in file systems, and coordinating input/output devices through drivers and other system components. The OS presents higher-level abstractions—such as files, processes and network connections—so applications need not control each hardware device directly. It also supplies interfaces: people may use a graphical desktop or a command line, while programs request operating-system services through programming interfaces.

The kernel is the central part of an operating system that performs or coordinates privileged work, including access to processors, memory and devices. Other components, such as graphical interfaces and system services, may run outside the kernel. This division differs among operating systems. In Windows, for example, applications generally run in user mode and core operating-system components run in kernel mode. Restricting what an application can access helps isolate processes and protect system data; code running in kernel mode has broader access, so a serious error in a kernel-mode component can affect the whole system.

Operating systems are designed for different kinds of machines and workloads. Desktop and mobile systems support interactive use and general applications; server and mainframe systems emphasize shared services and large-scale processing; embedded operating systems manage devices with specialized tasks; and real-time systems are designed for workloads with timing requirements. These labels describe overlapping design goals rather than a single rigid taxonomy: one system may serve several roles, and the needs of a car controller, smartphone and data-centre server differ substantially.

Early computers often relied on small supervisory programs and batch processing to coordinate jobs. As hardware and use expanded, operating systems developed support for multiprogramming, interactive time-sharing, multiple users and graphical interfaces. IBM introduced OS/360 for the System/360 family in 1964, seeking to provide a common software environment across its mainframes. At Bell Laboratories, Ken Thompson and Dennis Ritchie began building Unix on a PDP-7 in 1969. Unix became an influential time-sharing system; its portability and design ideas helped shape later operating-system families and tools.

Operating-system design involves trade-offs. A system must share limited resources while remaining responsive, support its hardware and applications, and prevent one program from interfering with another. Security updates and permissions help address vulnerabilities, but they cannot remove every risk; bugs in drivers, applications or system components can still cause failures or expose data. Designers also consider reliability, accessibility, power use and how long devices can receive updates. Because operating systems mediate between software and hardware, changes to one layer can affect compatibility across an entire computing system.