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One of the signature features in Windows 8.1 is a major expansion of the built-in search capabilities. Click the Search charm to open a search pane on the right. Enter a search term and some results appear immediately beneath your input. If you don't find what you're looking for, click the search button (or press Enter) to see a complete list of results, including installed apps, settings, and results from the web.
If you're firmly convinced that Google is better than Bing, you can disable the Bing results and just use the search tool for local files, apps, and settings. But I've found the results generally excellent, and pressing the new system shortcut for Search, Windows key+S, is now second nature for me.
Enhanced multi-monitor support
Windows 8's support for multi-monitor configurations was severly limited, with no ability to mix immersive apps and desktop apps on a display. Windows 8.1 vastly improves this capability. You can now snap immersive apps (a Twitter feed, tracks in a music playlist, your email message list) alongside desktop apps on any monitor, with the ability to show the Start screen on either display.
New features aimed at the enterprise
One common rap on Windows 8 was that its features were aimed at consumers, with little to appeal to the traditional Microsoft base of enterprise customers. That changes in a big way with Windows 8.1, which introduces several new features designed for use with Windows-based corporate networks.
One of the most interesting new features is Workplace Join, which allows users to register personal devices on the corporate network using Active Directory, without having to join the domain. (In fact, Workplace Join can be used on the standard edition of Windows 8.1, which doesn't support domain join. It also works with iOS devices.) Think of Workplace Join as a form of two-factor authentication. Users can access sensitive corporate resources, but only from a device that's been registered with the network and is subject to some basic device management policies.