Windows 8.1

Windows 8.1 is an operating system by Microsoft. It is a free upgrade for existing Windows 8 users. It replaced 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, as running on these processors will result in a bugcheck with error code 0x5D.

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.

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.

RTM

 * The Start button was brought back (although it still leads to the Metro start screen).
 * 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, you can re-enable it by right-click on the navigation pane and choose "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.
 * 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, Windows shows a title bar 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.
 * A power button has been added next to the search button on the start screen.
 * 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.