What controls the way in which the computer system function and provides a means by which users can interact with the computer.

A computer needs software that manages its hardware resources and gives the user a way to interact with the machine, and this role belongs to the operating system.

The operating system controls how the processor, memory, storage devices, and peripherals work together, schedules which programs run and when, and provides the interface, such as a desktop, icons, and menus, or a command line, through which a user gives instructions to the computer and receives feedback. Without it, application software would have no consistent way to access hardware, and the user would have no means of communicating with the machine at all.

Application software, like a word processor, depends on the operating system rather than controlling the whole system, the internet is a network of connected computers rather than software running on one machine, and the control unit is a hardware component inside the CPU, not the software layer that manages the whole system and its user interface.

Exam tip: whenever a question combines "controls how the system functions" with "lets users interact with the computer" in the same description, it is describing the operating system.