 I'm Tom Warren with The Verge. Apple has Siri, Google has Google Now, and Microsoft finally has Cortana. Cortana is a personal digital assistant for Windows Phone 8.1, a big update to Microsoft's mobile operating system. She takes the form of a circular icon, and you can talk or type to Cortana to get her attention. She's like your very own assistant, and she even has a notebook just like a real one. The notebook feature is designed so that only you can share information with Cortana, but she'll be learning about your habits and interests all the time before asking you to store anything she learns about you. Like Google Now and Siri, Cortana will answer basic web searches using natural voice commands. You can ask things like, how tall is Britney Spears? Five feet, four inches tall. Or what's the nearest restaurant? I found this restaurant. The difference here is that once you've completed a query, there's a multi-step element with Cortana where you can also say, call it, and she will understand you meant the nearby restaurant. You can also say, show me directions. Cortana also has a personality, and Microsoft has brought in the voice of Cortana from Halo, Jen Taylor, to answer some queries. Whether it's you asking, who is your father? And getting this reply. Technically speaking, that'd be Bill Gates. No big deal. Or do you like Siri and getting an equally witty result? Hard to say. So far, our conversations have been kind of one-sided. As Cortana is a personal assistant, she'll also notify you of things like sports scores or flight information. But you can also ask her to remind you in clever ways. Remind me when I next speak to my girlfriend that I need to discuss Kevin. Next time you talk to Sarah Elizabeth Hipple, I can remind you to discuss Kevin. Great. Cortana will then create a reminder that triggers when you next speak to your girlfriend. That's useful and super powerful. Other commands include the ability to ask Hulu to find the latest episode of a TV show, or just ways to turn off airplane mode and other system settings. Cortana is always with you in your pocket and learning about you. But the real trick for Microsoft will be when it can offer this type of digital assistant everywhere. In your living room, car, at work, and on every device you own. Cortana is powered by Bing, and it's impossible to imagine her existing without Microsoft's clever search work and servers crunching data in the background. Microsoft is rolling out Cortana to Windows Phone and Bing.com initially. One day you'll be able to ask Cortana to sing you a song, and her voice will be everywhere. Here's one I know. Should old acquaintance be forgot and never thought upon?