Wikipedia says DirectX is a collection of APIs for easily handling tasks related to game programming on the Microsoft Windows operating system. It is most widely used in the development of computer games for Microsoft Windows. The DirectX SDK is available free from Microsoft. The DirectX runtime was originally redistributed by computer game developers along with their games, but later it was included in Windows. Game developers still often include an updated version of DirectX that prompts installation automatically after the game installation to ensure proper program functionality.