Direct3D is designed to enable world-class game and interactive three-dimensional (3-D) graphics on a computer running Microsoft® Windows®. Its mission is to provide device-dependent access to 3-D video-display hardware in a device-independent manner. Simply put, Direct3D is a drawing interface for 3-D hardware.
You can use Direct3D in either of two modes: Immediate Mode or Retained Mode. Retained Mode is a high-level 3-D application programming interface (API) for programmers who require rapid development or who want the help of Retained Mode's built-in support for hierarchies and animation.
Microsoft developed the Direct3D Immediate Mode as a low-level 3-D API. Immediate Mode is ideal for developers who need to port games and other high-performance multimedia applications to the Microsoft Windows operating system. Immediate Mode is a device-independent way for applications to communicate with accelerator hardware at a low level. Direct3D Retained Mode is built on top of Immediate Mode.
These are some of the advanced features of Direct3D:
Developers who use Immediate Mode instead of Retained Mode are typically experienced in high-performance programming issues, and may also be experienced in 3-D graphics. Your best source of information about Immediate Mode is probably the sample code included with this SDK; it illustrates how to put Direct3D Immediate Mode to work in real-world applications.