This paper focus on a general-purpose FDTD-based solver, called general electromagnetic solver (GEMS), designed for modeling and simulating a wide variety of large-scale electromagnetic problems, involving microwave circuits, RF and digital electronic packages, as well as open region radiation and scattering problems. We begin by observing that there is a rapidly growing trend in computational electromagnetics (CEM) that is significantly impacting the computing landscape, namely the use of highly-parallel computers to address large and complex problems.