I have a Fortran95 program that I run on my Windows laptop (i7 2.0Ghz); its in serial, so its running on one thread, which seems consistent with task manager results (12.5% processor usage), so I figure it should be using ~1 ghz. Im compiling using the standard one that came with my F95 download and it takes about 22 minutes. Now I'm trying to run it on a RedHat computer; I just use the terminal to compile it (>gfortran FileName) then run it in the terminal and it takes more than 50 minutes. I poked around and found out its 2.8 Ghz pentium 4 in there. The system monitor says 100% usage for one core (which I assume is the hyperthreading), so by my rudimentary math thats 1.4ghz for the program. I understand this is a gross simplification, but I just dont understand how there can be 100-150% discrepancy. Linux and programming newb btw, so feel free to suggest some obvious thing I'm missing.