What Is Microsoft Windows?

Microsoft Windows is a family of operating systems developed by Microsoft Corporation that provides a graphical user interface, memory management, process scheduling, file system access, and hardware abstraction for personal computers, servers, and embedded devices. Windows is the dominant desktop operating system globally, running on the majority of personal computers, and its server variants power a large share of enterprise data centers.

Windows traces its lineage to two parallel development streams. The consumer-oriented line began with Windows 1.0 in 1985 as a graphical shell over MS-DOS. The enterprise-grade New Technology (NT) line, designed from scratch, shipped as Windows NT 3.1 in 1993. The NT architecture, built around a preemptive, reentrant microkernel with a hardware abstraction layer (HAL), became the basis for all subsequent Windows releases, including Windows XP, Vista, 7, 10, and 11.

Kernel and System Architecture

The Windows NT kernel follows a modified microkernel design that places core services such as process management, memory management, I/O management, and the security reference monitor in kernel mode, while subsystem environments run in user mode as discrete processes. A hardware abstraction layer sits between the kernel and the physical hardware, enabling Windows to run on multiple processor architectures, including x86, x64, and ARM, with minimal platform-specific code changes.

As described in the paper on the Windows NT kernel architecture published in IEEE Computer, extensions to the executive and kernel were required to support features such as Plug and Play, job objects, and 64-bit large memory addressing. The executive, which runs in kernel mode, contains subsystems for object management, virtual memory, I/O, cache management, and the security reference monitor. The Win32 subsystem, running in user mode, provides the programming interface that most Windows applications target.

Security Model

Windows implements a security model based on discretionary access control (DAC) and, in newer releases, mandatory integrity control (MIC). Every process runs under a security token that encodes the user's identity and privilege level. Before any access to a secured object, such as a file or registry key, the security reference monitor compares the token's privileges against the object's access control list.

Windows cryptographic components have undergone formal validation under FIPS 140-2 through the NIST Cryptographic Module Validation Program. Features such as BitLocker full-disk encryption and Windows Hello credential storage use the Trusted Platform Module (TPM) to bind cryptographic secrets to specific hardware, reducing the risk of credential theft when a machine is offline or stolen. User Account Control (UAC), introduced in Windows Vista, requires explicit elevation for administrative operations, limiting the blast radius of software that runs with standard user privileges.

Windows Ecosystem

Windows supports a broad application ecosystem through several programming interfaces. The Win32 API, first stabilized in the 1990s, remains the foundation for a large share of desktop applications. The Universal Windows Platform (UWP) model, introduced with Windows 10, defines a sandboxed execution environment for apps distributed through the Microsoft Store. The Windows Subsystem for Linux (WSL) runs a Linux kernel image alongside the Windows kernel, allowing developers to run Linux command-line tools, compilers, and servers directly on a Windows machine without a separate virtual machine.

Applications

Microsoft Windows has applications in a range of fields, including:

• Enterprise desktop computing, as the primary managed endpoint platform in most corporate environments
• Server infrastructure, hosting web servers, databases, Active Directory, and .NET applications
• Industrial control and human-machine interface (HMI) systems in manufacturing
• Scientific computing, running simulation and data analysis software developed for Windows toolchains
• Game development and delivery, through DirectX graphics APIs and the Xbox platform