Consider two computers with different hardware and software configurations. When running the exact same serial Navier-Stokes code on each platform it takes x and y time to execute one iteration for computer 1 and 2, respectively. In this case, $\Delta = x-y$, is the iteration time difference between computer 1 and computer 2.
What could be the impacting the magnitude of $\Delta$? One obvious candidate is the CPU, my main question is whether there are other factors that could be impacting $\Delta$ on the same order as the hardware difference between CPUs?