Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Windows Runtime, or WinRT, is Microsoft's 2011 programming model that forms the backbone of the new Metro-style apps in their new Windows 8 operating system. WinRT supports development in C++ and the managed languages C# and VB.NET, as well as JavaScript. Programs can be written using Windows Runtime that will run on both the Intel and ARM editions of Windows 8 without modification. WinRT is essentially a COM-based API, although relying on an enhanced COM. Because of its COM-like basis, WinRT allows relatively easy interfacing from multiple languages, just as COM does, but it's essentially an unmanaged, native API. The API definitions are, however, stored in ".winmd" files, which are encoded in ECMA 335 metadata format, the same format that .NET uses with a few modifications.