WINDOWS VISTA:
Multimedia Class Scheduler (MMCSS): more glitch-resistant audio playback
The Multimedia Class Scheduler service allows multimedia applications to register their time-critical processing to run at an elevated thread priority, thus ensuring prioritized access to CPU resources for time-sensitive DSP processing and mixing tasks. You can think of this as anti-glitch insurance against other, non-audio-related processes running on your computer competing for CPU. Basically, with MMCSS you minimize interruptions or glitches in audio playback even when running other applications in the background.
