DirectX 9.0c June 2010 Update for Windows Operating Systems
DirectX is a group of technologies designed to make Windows-based computers to be able to run and display applications rich in multimedia elements such as the colors in the image, video, 3D animation, and audio. DirectX also has its own security and performance updates, along with many new features available from all technologies, which can be accessed by applications using the DirectX APIs.
Sometimes some applications and games require DirectX application in DirectX This is because there are some drivers that do not exist in Windows or other programs.
The latest version of the Microsoft Windows Gaming API Microsoft has given its new powers, namely the High-Level Shader Language (HLSL) to support the features of the most advanced design tools for the development of multimedia elements such as full color stunning graphics, 3D animation video and audio capabilities course has been refined.
DirectX 9.0 also introduces significant improvements across the API (Application Programming Interface). Start of DirectSound that offers the latest audio capabilities, DirectShow that accelerates video rendering hardware inside, and Direct3D which improves graphics programmability with new models such as the program vertex and pixel shader 2.0.
That's a little explanation about DirectX if you do not already have an application DirextX 9.0c Update June 2010.