Windows 8.1

Windows 8.1 is an operating system by Microsoft. It is a free upgrade for all Windows 8 users. It replaces Windows 8 and was succeeded by Windows 10 on 29 July 2015. This is the first version of 64-bit Windows to drop support for processors without the CMPXCHG16b, PrefetchW and LAHF/SAHF instructions, for as running on these processors will cause an  bugcheck upon boot.

Although the operating system was marketed by Microsoft as an update for Windows 8, Microsoft's traditional support policy treats Windows 8.1 as a service pack.

As of July 2022, it runs on 2.86% of desktop and laptop computers.

It is the last release of Windows to have support for Windows Media Center as Microsoft discontinued support for the application with the release of Windows 10. It is also the last release of Windows to have the ability to create MS-DOS 8.00 startup disks, and thus to include MS-DOS in any form and to ship with a DVD release, since physical retail copies of Windows 10 and later ship with an USB mass storage device.

RTM

 * The Start button was brought back (although it still leads to the Metro start screen).
 * The "All Apps" view was added to the Start screen.
 * Added Device Encryption for compatible hardware.
 * Added support for 3D printing.
 * Added support for Wi-Fi Direct, Miracast, tethering and NVMe.
 * Text and GUI elements can now scale up to 200%. Additionally, scaling settings can now be setup independently on each display in multi-monitor configurations.
 * Computer is renamed to This PC.
 * Clicking the File Explorer icon in the taskbar takes you to This PC instead of Libraries, unlike in Windows 7 and 8. Additionally, Libraries is disabled by default, but it can be re-enabled by right-clicking on the navigation pane and choosing "Show libraries" or "Show all folders".
 * User folders (Desktop, Documents, Downloads, Music, Pictures, Videos) added to This PC.
 * The Windows Experience Index has been removed. However, the command-line tool to determine the rating values (WinSAT) is still included.
 * The Backup and Restore Control Panel applet has been removed in favor of File History.
 * New set of default wallpapers.
 * New customization options for the Start screen.
 * New Metro applications introduced, with many existing ones updated.
 * Redesigned PC Settings.

Update 1 (on non-touch devices)

 * When you hover over the top of a Metro app, a title bar appears with minimize and close buttons.
 * Right-clicking on the Start screen opens up a menu instead of the touch-oriented controls at the bottom.
 * The "Go to the desktop instead of Start when I sign in" feature in Taskbar and Navigation Properties first introduced in the original release is now enabled by default.
 * You can pin Metro apps to the taskbar.
 * Power and Search buttons has been added to the start screen.
 * It's also possible to enable the power button on a tablet by going to  registry key, then create a new DWORD value named   and set it to 1, then restart explorer.exe.
 * Added dividers between apps in the "All Apps" view in Start.
 * SkyDrive is renamed to OneDrive (you can also get this in Windows 8 and Windows 8.1 RTM (without Update 1) by updating the SkyDrive app via the Store).
 * The default media player and photo viewer has been changed to Windows Media Player and Windows Photo Viewer respectively.

System requirements
Microsoft recommends Windows 8.1 to be installed on a system with a processor with a speed of at least 1 GHz, at least 1 GB (2 GB for x64 versions) of RAM, 16 GB (20 GB for x64 versions) of hard drive space, a DirectX 9-based WDDM display adapter or better display adapter. Windows 8.1 drops support for x64 processors without the CMPXCHG16b, PrefetchW and LAHF/SAHF instructions, as attempting to boot on these processors will cause an  bugcheck.

Windows 8.1 can be installed on processors as early as the Pentium 4. The x64 version of Windows 8.1 can be installed on processors as early as the Athlon 64 with Socket AM2. Windows 8.1 can also be run with as low as 512 MB of RAM.

Hardware compatibility
Windows 8.1 is officially compatible with Intel processors up to Skylake (6th Generation). On Kaby Lake (7th Generation) up to Coffee Lake (8th/9th Generation), 8.1 is not supported due to a lack of Windows Update and Intel Graphics, however, hacks have been made to get both working. For Ice Lake (10th Generation) up to Alder Lake (12th Generation), no known hacks have appeared for Intel Graphics, but the chipset drivers for Ice Lake, Tiger Lake (11th Generation), and Alder Lake have been confirmed to install without any issues.