When the iPhone app is built, the Xamarin C# compiler generates C# Intermediate Language (IL) as usual, but it then makes use of the Apple compiler on the Mac to generate native iPhone machine code just like the Objective-C compiler. The calls from the app to the iPhone APIs are the same as though the application were written in Objective-C. For the Android app, the Xamarin C# compiler generates IL, which runs on a version of Mono on the device alongside the Java engine, but the API calls from the app are pretty