DirectX 9.0b is an updated version of the DirectX 9.0 runtime which includes bug fixes and improves performance in the graphics and networking components. There are no new or modified APIs in this release.
Microsoft DirectX is a group of technologies designed to make Windows-based computers an ideal platform for running and displaying applications rich in multimedia elements such as full-color graphics, video, 3D animation, and rich audio. DirectX 9.0b includes security and performance updates, along with many new features across all technologies, which can be accessed by applications using the DirectX 9.0 APIs.
Follow the download tab above to download, once downloaded the installer itself will download the update.