The Microsoft® DirectX™ 2 Software Development Kit (SDK) provides a finely-tuned set of application programming interfaces (APIs) that give you, as a developer, the resources needed to design high-performance, real-time applications, such as the next generation of computer games and multimedia applications.
Microsoft developed the DirectX 2 SDK for a number of reasons. The primary reason is to make performance on Windows-based platforms rival or exceed performance on MS-DOS-based platforms and game console-system platforms. Other reasons are to promote game development for Microsoft Windows®, and to assist you by providing a robust, standardized, and well-documented platform for which to write games.