Windows RT 8.1 is a special edition of Windows 8.1 designed for ARM-based devices (like the Surface RT, Surface 2, Nokia Lumia 2520, and some Samsung and Dell tablets). Unlike standard Windows 8.1, it cannot run traditional x86/x64 desktop applications—only "Modern UI" (Metro) apps from the Windows Store and a few bundled Microsoft apps (Office 2013 RT). The ISO Question: Official vs. Reality Officially, Microsoft never released Windows RT 8.1 as a downloadable ISO for general users. Unlike standard Windows, RT was preinstalled on devices and updated via Windows Update . There is no legitimate retail ISO to install Windows RT 8.1 from scratch on any ARM device.