The sample audio driver is a layered, interrupt-driven stream interface driver that drives a built-in audio device. The layers are the typical MDD and PDD layers that native device drivers use, although the Device Driver Interface (DDI) functions in the MDD layer are the same as the stream interface functions used by ordinary stream interface drivers. This code is provided as a convenience and does not imply any restrictions in the way audio hardware for Windows CE must function. An audio driver could be implemented that is monolithic, is polled, and drives a peripheral device, if desired. The sample audio driver’s MDD layer implements a single audio device capable of playing and/or recording pulse code modulation (PCM) waveform audio. The sample supports simultaneous recording and playing but may also be used with audio devices that can only perform one of those functions at a time. The PDD layer is responsible for communicating with the audio hardware to start and stop playing and recording and to initialize and de-initialize the hardware.