Windows 8 Extreme Edition R2 2013 64 Bit
while windows 8.1 is not the only update for windows 8, it does have the most significant updates to the previous release of the operating system, and is the only update to windows 8 that has been released for the 64-bit version of windows 8.   the new user interface (ui) of 8.1 is based on the windows phone 7 and windows phone 8 versions of the operating system, which were released in 2012. it has an overall design and aesthetic which is similar to microsoft’s own metro design language. 
the new features of the operating system include a refreshed start screen, a new search experience, a refreshed start menu, the action center, a new notification system, a new browser, and an updated method of multitasking. the start screen has been reorganized into four columns, with the left and right columns containing tiles which can be “pinned” to the start screen. the top and bottom rows contain the settings, while the left and right are reserved for apps. like the windows phone ui, the start screen can be personalized to display the apps, contacts, music, and photos that are most relevant to the user.  
windows 8.1 has been released as a free update for windows 8 users. according to microsoft’s official statement, windows 8.1 will be installed on all existing windows 8 pcs. this includes windows rt tablets and windows 8-based windows phones. the update will be available starting april 8, 2014.
windows 8.1 brings additional integration with windows phone 8.1, with the addition of a number of common features across the two platforms, including support for multitasking with split screen apps and a new message preview pane within mail, the improved photos app, and better integration with the windows phone camera. windows phone 8.1 can also be used as a desktop pc running windows 8.1, and provides access to a number of microsoft services, including skydrive. these include a new system-level app that allows users to access their windows phone contacts, and an improved skype app, which is expanded to include a client for windows phone and a second tab to display contact information.    windows phone 8.1 features a redesigned interface, and adds support for a number of additional features, including a highly optimized browser, better integration with office (including onenote and excel), a visual search tool, and integration with microsoft’s yammer social network app.  windows phone 8.1 is marketed as a more business-oriented version of windows phone, as it includes support for system center 2012 configuration manager. 
windows 8.1 is also the first version of windows to feature the windows store. the windows store is a portal for searching for, buying, and downloading apps for use on windows. while the desktop version of windows was previously the only windows version to include an integrated software store, the windows store now allows users to install apps on the windows desktop and windows phone. in addition to the new store interface, windows 8.1 also includes a new version of internet explorer that is more akin to the current version of internet explorer for windows phone. apps and other content can be synchronized to the windows phone from the pc via skydrive, and the windows phone app can also synchronize apps to windows 8.1.