[LBXZero]

The performance between windowed mode and full screen mode depends on the hardware, drivers, and the operating system.

In my computer hardware and OS classes, we talked about the difference between interrupts and polling for system status control. The difference between windowed mode and fullscreen mode is about the same concept.

The difference is that in fullscreen mode, the system tries to keep a smooth pace, while in windowed mode the system is not holding pace. Try going into dxdiag.exe and run the DirectDraw diagnostics and watch the speed of the bouncing box between fullscreen and windowed.

Also for the performance between switching programs in alt-tab, some programs are put in a background state and may be shoved into virtual ram while WoW is running in fullscreen to give the primary program more room. In windowed mode, those visible programs do not go into background mode and stay in RAM.