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The NFB X server model defines the larger, more generic portions of the server but it makes no assumptions about the capabilities of the graphics chips and adapters that must eventually interact with the DDX layer. For example, the standard server DDX layer implements graphics primitives with a set of pixblit routines that address the requirements of monochrome frame buffers or color frame buffers. These sample implementations are not well suited for the intelligent graphics adapters using chips or chip sets with more extensive capabilities.
The NFB layer provides a simple interface to a second set of graphics primitives that are not dependent on a frame buffer-oriented display driver and provide more efficient access to advanced graphics cards.
The NFB API does incur small performance costs, although in most cases these are more than offset by the server optimizations that can be easily implemented for different types of adapters.