PMP was a fortress. It dictated that if you wanted to play a premium movie, the operating system would load a special kernel-mode driver ( drmkaud.sys and related components), enter a "Protected Process," and encrypt the audio/video stream all the way to the graphics card and monitor. The CPU, the memory, and the bus were supposed to be sealed tight. If the OS detected a debugger or an unsigned driver, playback would halt. It was the digital equivalent of a sealed room.