Most crucially, Cortana handles all search functions for the operating system--and she has a few tricks up her sleeve.
First of all, Cortana doesn't only search your local files and system settings, but also the web, the Windows Store, and any files stored in the OneDrive cloud storage associated with your Microsoft Account. Finding your personal files about a topic takes a few extra clicks, however. Searching for something basic like "Windows 10" shows Bing search findings by default--even if you have a ton of pictures and documents about Windows 10. You'll need to click on the "My stuff" button at the bottom of Cortana's search suggestions--which unfortunately can't be set as a default--to scour your local files.
Unless you take advantage of Cortana's awesome natural language search support, that is.
Cortana groks commands you issue in natural language, so saying "Find pictures from June" or "Find documents about Windows 10" will immediately scan your files for matching results. You can even get fancy, mixing and matching modifiers with searches like "Find documents about Windows 10 from June."
Cortana can also schedule reminders for you, tied not just to specific times but also specific locations (pulled from the Maps app) and contacts (pulled from the People app). When you tie a reminder to a location, it'll appear the next time you visit the place, while contact-based reminders kick in the next time you communicate with the person.
You can set reminders two ways: By opening Cortana and clicking the light bulb "Reminder" icon in the left-hand pane, or by once again using natural language commands starting with "Remind me to..."
For example, you could say "Remind me to call Mom Friday at 5" or "Remind me to get my keys when I'm home" and Cortana will intelligently handle the dirty work, asking you to verify that the details are correct. If you say something like "Remind me to pick up eggs at the supermarket," Cortana will locate the nearest one and ask if that's the location you're asking about, allowing you to tweak it if not.
Alas, Cortana doesn't handle people-based reminders very well with natural language. Saying "Remind me to tell Jennifer about eggs" results in a reminder with "Tell Jennifer about eggs" as the status, and nobody filled in as the contact.
Need to wake up? Cortana can set proper alarms with commands like "Set an alarm for..." and "Wake me up in 30 minutes," too.
Notifications and cards
Cortana pulls information from your various connected accounts to pop up notifications from time to time. If you have a meeting or event scheduled that day, for example, it'll appear at the top of the "at a glance" card interface that appears whenever you open Cortana. (Cortana can also theoretically tell you when it's the best time to leave for a scheduled event based on traffic conditions, but I've yet to see that work in practice.)
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