Direct3D Immediate Mode is Microsoft's low-level 3D API. It allows you to port games and other high-performance multimedia applications to the Windows operating system.
Immediate Mode is a thin layer above real-time 3D accelerator hardware that gives you access to the features of that hardware. It also offers optimal software rendering for some hardware features that are not present. Immediate Mode gives you the flexibility to exploit your own rendering and scene management technologies. It is a device-independent way for applications to communicate with accelerator hardware at a low level, enabling maximum performance.
Unlike Retained Mode, Immediate Mode does not provide a geometry engine; applications that use Immediate Mode must provide their own object and scene management. Therefore, you should be knowledgeable in 3D graphics programming to use Immediate Mode effectively.
Direct3D is based on the OLE Component Object Model (COM), and is tightly integrated with DirectDraw. Microsoft will incorporate Direct3D into a future version of Windows. For more information, see Introduction to Direct3D Immediate-Mode Objects.