Most systems will not have any sort of external media - no floppy drives, no removable hard disks, no cd burners. USB ports will be filled with epoxy and any peripherals will also be physically secured to their ports. Wherever possible drivers for external media will simply be removed from the OS installation image for those systems.

That will leave a handful of system that do have external media. Those will have extreme access restrictions - at a minimum account restrictions and audit logs that will be regularly correlated with a hand-written log that contains timestamps and signatures of both people. They may even put the system in a room with keycard access that requires two different keycards and associated PINs to be entered before the door opens.