Which layer of an operating system is at the topmost level?

The application layer is considered the topmost level of an operating system. This layer is where user applications operate, and it interacts with the system services provided by the underlying layers. It serves as the interface between the end-users and the system, allowing users to execute programs and perform tasks such as running software applications, processing data, and interacting with files.

Because user applications are designed to utilize the functionality provided by the operating system, they rely on lower layers—like the service layer, which provides core functionalities, and the kernel layer, which manages hardware resources. The application layer's proximity to the user makes it crucial for user experience, and it often includes graphical user interfaces (GUIs) that allow for easier interaction with the underlying system components.

The other layers serve specific foundational roles, supporting the application layer rather than acting as the interface through which end-users engage with the system. Therefore, the distinction of the application layer as the topmost level highlights its direct interaction with the users and its role in executing user-oriented tasks.