There have been a number of comments about the precision of the standard timing routines available in ifort.
I have written a simple example which differenciates between the apparent precision of system_clock, given by Count_Rate, and the actual precision available from the different values returned.
I have run this example on ifort Ver 11.1, which I have installed.
It shows that both CPU_TIME and SYSTEM_CLOCK have only 64 ticks per second, which is very poor precision available via the Fortran standard intrinsic routines.
Better precisoin is available ( see QueryPerformanceCounter) and should be provided in these intrinsic routines.