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
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.
a
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.
oS SR stands for "operating system service request." It typically refers to a formal request for assistance or action related to the operating system of a computer or network. This can involve issues such as software malfunctions, updates, or enhancements needed to improve system performance or security. In a broader context, it may also relate to IT service management processes.
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.