@nuhi i happened to disable most device drivers in vista e.g. display, network, sound and still the latency was hovering at average of 1000 us with a max of 20000 us (peaks when aero/network/sound drivers are enabled or disabled. These peaks do not show in DPCLAT in XP while changing resolutions/colordepth/enabling or disabling drivers.) Also getting rid of the peaks and troughs of DPCLAT in vista while enabling/disabling aero/other drivers could lead to a more stable vista besides increasing performance. This leads me to believe getting an XP like under 100 us latency score in DPCLAT program could still be a good idea. There is more to the latency than device drivers and hardware. This is the direction which could be explored more.