Abstract: An object-oriented framework is introduced for coupling device drivers to an application program. Two class trees are introduced: the first class tree comprises the device drivers. The device drivers actually exchange messages with the IO devices. They depend on the protocol used, on the IO interface, and on the operating system. The second class tree comprises the so-called physical objects. Their task is to define parameters that are necessary to describe what an IO device is supposed to do. The parameters only depend on the device's functionality, but not on the protocol, the IO interface or the operating system. In order to couple a physical object with a device driver, the physical object holds a pointer to its device driver. The connection is an “object reference,” and therefore, the active device driver may be changed at runtime.