According to MS, the Windows Key searches ALL apps, files, and settings:
You can press the Windows logo key +S to open Search. To search for a file on your PC or SkyDrive, press the Windows logo key +F. And to search for settings on your PC, press the Windows logo key +W.
To change the scope of your search
By default, the Search charm searches the apps, files, and settings on your PC and SkyDrive, plus the web. But you can choose to search for only one type of result, like settings, files, images on the web, or videos on the web. And if you're in an app when you open Search, you can choose to search only that app (this might not be available in some apps).
Swipe in from the right edge of the screen, and then tap Search.
(If you're using a mouse, point to the upper-right corner of the screen, move the mouse pointer down, and then click Search.)
Tap or click the arrow
, then tap or click the scope you want to use.
To change search settings
You can delete the search history that's stored by the Search charm, choose how much of your search info is shared with Bing, and filter adult content out of your web search results.
Swipe in from the right edge of the screen, tap Settings, and then tap Change PC settings.
(If you're using a mouse, point to the upper-right corner of the screen, move the mouse pointer down, click Settings, and then click Change PC settings.)
Tap or click Search and apps, then tap or click Search. All of the settings for the Search charm are here.
This looks useful also: