Does Windows Phone 7 app runs on Windows Phone 8?

Question

Does Windows Phone 7 app run on Windows Phone 8?

Can someone just go to app store with a WP8 and download an app that was built to Windows Phone 7?

Does a simple "hello world" app works in that way without compability issues?

Answer 1

Of course it works. For example, Windows Phone 8.1 is able to run both Windows Phone 7.X and Windows Phone 8 applications.