Windows RT, the only edition of Windows 8 for systems with ARM processors, only supports applications included with the system (such as a special version of Office 2013), supplied through Windows Update, or Windows Store apps, to ensure that the system only runs applications that are optimized for the architecture. Windows RT does not support running IA-32 or x64 applications. Windows Store apps can either support both the x86 and ARM architectures, or compiled to support a specific architecture.
What Windows version is compatible with ARM processors? What apps work on Windows RT? Why does Windows RT only work with apps included with the system?