Both of the solvers can run on parallel computers or clusters to achieve faster run times and/or run larger problems. If a model only has lossless boundary conditions and materials, then the resulting eigenproblem is real, that is, the finite-element matrix and eigenpairs contain only real numbers. If any loss is present in the model, or periodic boundary conditions are applied, the problem will be complex. Real problems are generally solved much more rapidly than complex problems, and they require less memory for a given mesh.
To speed up simulation run time and reduce project file size, you may suppress field output as described in “Fields”.