Windows RT is an operating system for mobile devices developed by Microsoft, primarily for tablet computers but also for convertibles. It is essentially an edition of Windows 8.x built for the 32-bit ARM architecture (ARMv7). First unveiled as a prototype in January 2011 at Consumer Electronics Show, the Windows 8 RT operating system was officially launched alongside Windows 8 on October 26, 2012, with the release of three Windows RT-based devices, including Microsoft's Surface tablet. Unlike Windows 8, Windows RT is only available as pre-loaded software on devices specifically designed for the operating system by OEMs.Microsoft intended for devices with Windows RT to take advantage of the architecture's power efficiency to allow for longer battery life, to use system-on-chip (SoC) designs to allow for thinner devices, and to provide a ""reliable"" experience over time. In comparison to other mobile operating systems, Windows RT also supports a relatively large number of existing USB peripherals and accessories, and includes a version of Microsoft Office 2013 optimized for ARM devices as pre-loaded software. However, while Windows RT inherits the appearance and functionality of Windows 8, it has a number of limitations; it can only execute software that is digitally signed by Microsoft (which includes pre-loaded software and Windows Store apps), and it lacks certain enterprise-oriented features. Windows RT was released to mixed reviews from various outlets and critics. Some felt that Windows RT devices had advantages over other mobile platforms (such as iOS or Android) because of its bundled software and the ability to use a wider variety of USB peripherals and accessories, but the platform was criticized for its poor software ecosystem, citing the early state of Windows Store and its incompatibility with existing Windows software, and other limitations over Windows 8.Critics and analysts deemed Windows RT to be commercially unsuccessful, citing these limitations, its unclear, uncompetitive position of sitting as an underpowered system between Windows Phone and Windows 8, and the introduction of Windows 8 devices with battery life and functionality that met or exceeded that of Windows RT devices. Improvements to Intel's mobile processors, along with a decision by Microsoft to remove OEM license fees for Windows on devices with screens smaller than 9 inches, spurred a market for low-end Wintel tablets running the full Windows 8 platform that cannibalized Windows RT. Vendors quickly began phasing out their Windows RT devices due to poor sales, and less than a year after its release, Microsoft suffered a US$900 million loss that was largely blamed on poor sales of the ARM-based Surface tablet and unsold stock.Only two more Windows RT devices, the Microsoft Surface 2 and Nokia Lumia 2520 in late-2013, were released outside of the five original launch devices, and no Windows RT counterpart of the Surface Pro 3 was released due to a re-positioning of the Surface line into a high-end market, and a switch to Intel architecture for the Surface 3. These developments left Microsoft's future support of the platform in doubt. As of February 2015, with the end of production for both Surface 2 and Lumia 2520, Microsoft and its subsidiaries no longer manufacture any Windows RT devices.There is no equivalent to Windows RT for Windows 10, and Microsoft does not consider Windows RT devices to be compatible with Windows 10. Windows 10 Mobile, based on Windows Phone, was unveiled for use on tablets and smartphones with ARM architecture.