The basic model for OpenGL command interpretation is immediate mode, in which a command is executed as soon as the server receives it; vertex processing, for example, may begin even before specification of the primitive of which it is a part has been completed. Immediate mode execution is well-suited to interactive applications in which primitives and modes are constantly altered. In OpenGL, the fine-grained control provided by immediate mode is taken as far as possible: even individual lighting parameters (the diffuse reflectance color of a material, for instance) and texture images are set with individual commands that have immediate effect.
While immediate mode provides flexibility, its use can be inefficient if unchanging parameters or objects must be respecified. To accommodate such situations, OpenGL provides display lists. A display list encapsulates a sequence of OpenGL commands (all but a handful of OpenGL commands may be placed in a display list), and is stored on the server. The display list is given a numeric name by the application when it is specified; the application need only name the display list to cause the server to effectively execute all the commands contained within the list. This mechanism provides a straightforward, effective means for an application to transmit a group of commands to the server just once even when those same commands must be executed many times.