Operating system (OS)

In short: The operating system (OS) is the basic software of a computer. It manages hardware, memory and processes and offers programs and users a uniform environment. Examples: Windows, macOS, Linux, Android, iOS.

In more detail: The operating system mediates between hardware and applications. Programs need not know which hard drive or graphics card is installed but use standardized functions. The kernel makes this possible.

In Depth

Tasks:

• Process and thread management (scheduling): Distribute processing time, run programs in parallel.
• Memory management: Allocate RAM, virtual memory, isolate programs from each other.
• File systems: Files and folders on drives.
• Device drivers and input/output: Keyboard, screen, network, printer.
• Users and security: Accounts, permissions, login, encryption.
• Network: Connections, protocols.
• Interface: Graphical (GUI) or command line (CLI), shell.
• Services: Background programs, updates, printing, time.

Layers: Hardware → firmware (BIOS/UEFI) → bootloader → kernel → system services → interface → applications.

Common operating systems:

Area	Examples
Desktop	Windows 11, macOS, Linux (Ubuntu, Fedora), ChromeOS
Mobile	Android, iOS/iPadOS
Server	Linux (Debian, RHEL), Windows Server
Embedded/real-time	FreeRTOS, VxWorks, embedded Linux
Special	z/OS (mainframe), QNX (car)

Properties:

• Single/multitasking, single/multiuser.
• 32/64-bit (address width).
• Monolithic vs. microkernel.
• Real-time operating systems guarantee response times (industry, medicine).

Important terms: Kernel, driver, shell, file system, process, thread, service/daemon, registry (Windows), package manager (Linux).

Difference from firmware: Firmware is software in the device itself (BIOS); the operating system is started by it and lives on the drive.

Updates: Security updates are decisive. Systems no longer supported (end of life) are a risk.

See also: Kernel (operating system core), Drivers, Boot process of a Windows 11 computer