Operating System

An operating system (often abbreviated OS) is a foundational software that manages a computer's resources—including the processor, memory, storage, and input and output devices. It creates an interface between hardware and user applications, so that each application does not need to communicate directly with the hardware.

Nearly every computing device has an operating system: personal computers, servers, modern smartphones, and embedded systems. Well-known examples include Windows, macOS, Linux, Android, and iOS.

Core Functions

The operating system allocates processor time among running processes (process scheduling), enabling multiple applications to run simultaneously. It also manages memory, preventing one application from interfering with another's memory, and organizes storage in the form of a file system. Additionally, it controls peripheral devices through small programs called drivers.

Kernel and Layers

The core of the operating system is called the kernel, which runs at a privileged level and directly accesses the hardware. User applications run at a restricted level and request services from the kernel through calls known as system calls. Architectures vary: a monolithic kernel incorporates many services internally, while a microkernel delegates most services outside the core.

Types and Uses

Operating systems are categorized by their use: desktop systems, server systems, mobile phone systems, and real-time systems that must respond within strict time constraints, such as in automobiles and factories. Another category comprises multi-user systems, where different users can access a single machine simultaneously, each with different permissions.

Security and Users

The operating system enforces user separation through authentication, authorization, and file permissions. Security updates are part of ongoing maintenance, since kernel vulnerabilities can potentially allow an attacker to compromise the entire system.