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 similar to previous Service Packs of Windows.
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.