Int 2F Fn 4503  U - Microsoft Profiler (prof.com/vprod.386) - Start Profi  [G]

   AX = 4503h

Notes: Profiling is also turned on by the key combinations
     LeftShift + RightShift + Alt and LeftShift + RightShift + Ctrl
   for PROF.COM, this call programs the CMOS clock by reading register
     0Ch, and setting bit 6 of register 0Bh.  It then makes sure that IRQ8
     is unmasked

See Also: AX=4504h