from the offical document The DirectX SDK is broken into the following sections: DirectX Programming Guide DirectX Tools DirectX Samples DirectX Reference and another: What's New in DirectX 9.0 SDK Update (February 2005) API Updates Performance Tool Updates Technical Article Updates DirectX Component Status ============================ so I make a conclusion. the DirectX SDK sometimes do not include the DirectX API.because kit just a tool that help using the DirectX API. but sometimes when people said DirectX SDK ,they include the DirectX API in SDK. so Am I right? =============================== you see,I still confuse what is DirectX. now I have new idea about DirectX. it is product by the form of static lib or dynamic lib. it is LIB. it is not profound. it is not abysmal. it is not fathomlessit , not plumbless. it have common characteristic of lib. oh my god.before I surely know it is lib.but now I notice it is lib.thus I notice many other thing.it have many thing:function ,class ,struct,constant. but no variable:))(you notice it?) before I think directx is very complicate.it is un-imageable.