Windows 8 is a major release of the Windows NT operating system developed by Microsoft. It was released to manufacturing on August 1, 2012; it was subsequently made available for download via MSDN and TechNet on August 15, 2012,[6] and later to retail on October 26, 2012.[7]

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Windows 8 introduced major changes to the operating system's platform and user interface intended to improve its user experience on tablets, where Windows was now competing with mobile operating systems, including Android and iOS.[8] In particular, these changes included a touch-optimized Windows shell based on Microsoft's Metro design language and the Start screen, a new platform for developing apps with an emphasis on touchscreen input, integration with online services, and Windows Store, an online distribution for downloading and purchasing new software, and a new keyboard shortcut for screenshots.[9] Many of these features were adopted from Windows Phone. Windows 8 added support for USB 3.0, Advanced Format hard drives, near field communications, and cloud computing. Additional security features were introduced, such as built-in antivirus software, integration with Microsoft SmartScreen phishing filtering service and support for UEFI Secure Boot on supported devices. Windows 8 is the first version of Windows to support the ARM architecture, under the Windows RT branding. Windows 8 removed support for non-SSE2 CPUs and devices without NX.

Windows 8 was released to a mixed critical reception. Although reaction towards its performance improvements, security enhancements, and improved support for touchscreen devices was positive, the new user interface of the operating system was widely criticized for being potentially confusing and difficult to learn, especially when used with a keyboard and mouse instead of a touchscreen. Despite these shortcomings, 60 million Windows 8 licenses were sold through January 2013, a number that included both upgrades and sales to OEMs for new PCs.[10]

Microsoft released Windows 8.1 in October 2013, addressing some aspects of Windows 8 that were criticized by reviewers and early adopters and incorporated additional improvements to various aspects of the operating system.[11]

Windows 8 was ultimately succeeded by Windows 10 in July 2015. The server counterpart, Windows Server 2012, currently receives security updates until October 2023, and unofficial methods have been made to apply these patches to the original Windows 8.