For those of you that may not know, since the early days of windows objects on screen were rendered by the CPU. These objects were referred to as GDI objects. The CPU renders graphics much much slower than the GPU, so everything that is on screen by GDI is very slow and tears. Microsoft has partially fixed this problem with the implementation of Direct 3D (Aero UI) on the borders of windows and such. Aero allows windows to sync to the vertical blanking period, but the objects within the window rendered by GDI are not. This causes nasty tear and graphical imperfections when resizing windows.