Electromagnetic simulations' software is depending always on microprocessors and graphic cards and memories rather than operating systems, however, such simulations are greedy in flops so using grid computing on clouds or having your own clusters would be the right solution. But, if I answer your pertinent question, I would say that using HPC code for clusters is the solution, so the appropriate OS is that which allows you to get the most rapid output.

Hi,

what do you mean by Electromagnetic Simulations? Geant4?

In that case, I'd go for Linux.

Hi,

"Electromagnetic Simulations" is used in the question above, I think it's about HFSS or ADS when we try to compute S11, gain, .. of antennae or to simulate electronic cards and their electromagnetic compatibility problem.

Hi

For a good simulations, you focus on the hardware rather than the operating system unless if you are going to use a specific software that require special clusters that you may found it already installed or you still can add it to any of those operating systems.