d
The Operating System (OS) connects the user, applications, and hardware together.
System
Clusters and sectors relate to storage areas on a disk - not the operating system.
An operating system is a necessary concept of using a modern computer. It is not a matter of "popularity."
when it is needed
Operating system CD
a
The operating system provides a way for the user to manage system hardware and resources while providing a reasonably usable interface for the user to be able to use it.
embeded os works as a firmware and applies the concept of firmaware .
Operating systems as a concept aren't criticized by sensible people, as there is simply no viable alternative for what they do.
Both are software, operating system is software that will make your computer boot up and run. while Application software is a program that will run on a functional operating system.
Operating System level.