When the user moves the mouse, the system moves a bitmap on the screen called the mouse cursor. The mouse cursor contains a single-pixel point called the hot spot. This is the point that the system tracks and recognizes as the position of the mouse cursor. When a mouse event occurs, the window that contains the hot spot typically receives the mouse message resulting from the event. The window need not be active or have the keyboard focus to receive a mouse message.
The system maintains a variable that controls the mouse speed; that is, the distance that the mouse cursor moves when the user moves the mouse. You can use the SystemParametersInfo function with the SPI_GETMOUSE flag or SPI_SETMOUSE flag to retrieve or set the mouse speed.