Is your driver an IOAudio class? Godfrey At 19:19 -0800 01-11-20, Sean Morrell wrote: Actually, the driver is for an audio device. And the user space application is nothing more than a system preference pane, needed only to configure the device. The audio device has some pecularities making it unconfigurable using the typical CoreAudio interface. I do have the option of using an Audio HAL Plug-In. But I just wanted to see if another IPC method might quicken the development. At this time, I simply need a one way notification to the driver. Eventually the driver will need to respond to the preference pane, returning small structures of data. In both cases, what IPC would you recommend?