Complex sentence: The author does not go into any great detail about them, in a physical sense, though they seem to be hardware-based supercomputers of unknown size and computational ability, all of which are probably situated in safe, secure locations.
Split into simpler sentences: The author does not go into any great detail about them. Physically, they are hardware-based supercomputers, of unknown size or computational ability, all of which are probably situated in safe, secure locations.