Which describes the primary role of an operating system in a computer system?

• A. Directly executing all user applications without any system services.
• B. Loading only device drivers at startup.
• C. Isolating hardware from software so programs cannot interact with hardware.
• D. Managing hardware resources, running applications, and providing a user interface.

Answer: (D)

The operating system’s main job is to coordinate the computer’s resources, run applications, and provide a way for you to interact with the machine. It manages the CPU so programs can run—often at the same time—by scheduling time slices and keeping track of which program is using what resource. It handles memory allocation, storage access, and input/output devices, presenting a consistent interface to programs even though the underlying hardware can be complex. It also offers a user interface, whether graphical or command-line, so you can control and interact with the system.

This is the best description because it captures how the OS acts as a middle layer: it abstracts hardware details, provides essential services and system calls that apps rely on, and enables multitasking and safe, coordinated access to hardware. The other statements miss these responsibilities or misstate how software interacts with hardware—applications don’t run directly without OS services, the OS does more than just load device drivers at startup, and while it protects hardware access, it still allows controlled interaction through drivers and system interfaces.