The Microsoft DirectDraw Surface is the basic image unit in Microsoft DirectX graphics. It is either a rectangular collection of pixels of a particular width, height, and pixel format; or a buffer containing commands or vertices for Microsoft Direct3D. Surfaces have bits associated with them that denote their behavior and usage. These bits are called surface capability bits (or caps bits for short). Caps bits denote intended usages of their associated surfaces such as holding texels for rendering (the DDSCAPS_TEXTURE caps bit), being the target for 3D rendering (DDSCAPS_3DDEVICE), and many others. For more information about surface caps bits, see the DDSCAPS structure.
The primary surface is the surface that is currently being scanned out to the monitor by the display card. For more information about the primary surface, see the Flipping and Memory Configurations sections.