In the Windows 10 Anniversary Update, version 1607, Microsoft removed the on-off switch for Cortana. As with most things Windows, you can remove the search button or box completely if you're really convinced you won't use it. With that option set, you can still access Cortana's full feature set by tapping the Windows key and typing. If you want to turn off all of Cortana's features, leaving only the ability to search for local apps, files, and settings, you need to make a simple registry edit. On a system running Windows 10 Pro or Enterprise edition, you can use Group Policy to apply this setting across multiple machines in an enterprise network; on a single PC, use the local Group Policy Editor, gpedit.msc, to open the policy Computer Configuration Administrative Templates Windows Components Search Allow Cortana and set it to disabled.

Microsoft wants you to think of Windows 10 as a service, where new features arrive as they're ready, and where regular updates are themselves a feature. That's true in a sense, but Windows 10 is still Windows, a big and sprawling tangle of code that carries an implicit promise of backward compatibility. The "as a feature" part just means more frequent upgrades, which are now called "feature updates" to distinguish themselves from the cumulative monthly "quality updates." On July 29, Windows 10 celebrates the first anniversary of its release. Four days later, on August 2, a new upgrade - sorry, I mean feature update - will begin rolling out to the 350 million or so devices already running Windows 10.