Many computing device may now include two or more graphics subsystems. The multiple graphics subsystems may have different abilities, and may, for example, consume differing amount of electrical power, with one subsystem consuming more average power than the others. The higher power consuming graphics subsystem may be coupled to the device and used instead of, or in addition to, the lower power consuming graphics subsystem, resulting in higher performance or additional capabilities, but increased overall power consumption. By transitioning from the use of the higher power consuming graphics subsystem to the lower power consuming graphics subsystem, while placing the higher power consuming graphics subsystem in a lower power consumption mode, overall power consumption is reduced. A processor executes application software and driver software. The driver software includes first and second driver components for respectively controlling operation of the first and second graphics subsystems. A further proxy driver component routes calls (e.g. API/DDI calls) to one of said first and second driver components, in dependence on which of the first and second graphics system is in use.