An application runs in/on an OS. It is not the OS itself. Like Word or Chrome are applications.
Systems is too generic and not specific enough to mean anything in this context. Throw away answer.
Network Operating System does not 'usually' run on a hard drive but on memory chips in things like routers, wireless access points and switches that move network traffic.
Entry control loop. Because a while loop can be infinite or not based on whether Boolean given is T or F. So we need to know the preexisting condition before we can solve it.
