Cortana doesn’t want you to know where Master Chief is hiding. But for just about everything else, Microsoft's new voice-controlled personal assistant is ready and available to do your bidding. See also: Introducing Cortana, Plus 8 Other Things To Know About Windows 8.1 Cortana, a new feature in Microsoft’s Windows Phone operating system, is both a search engine and a helper, just like its counterparts: Apple's Siri and Google Now for Android.