Is the user interface a part of the operating system?

Answer 1

This answer depends on how technical your answer needs to be. The user interface ships with the operating system, so the average computer user might consider the user interface to be a part of the system. If you care to get technical, however, the user interface is not part of the operating system.

On all versions of Windows since at least 3.1, the graphical user interface is a module that runs atop the kernel, and is not actually part of the operating system. In fact, it can be swapped out for a different user interface, and the operating system will still run.

Similarly, you can remove the user interface, and the system will still operate (this is how some servers are configured; not loading a graphical interface can reduce memory and processor usage). Contrast this to a driver; if you remove a driver, the system will not run that hardware, thus, an installed driver becomes part of the operating system.

Technically, anything that runs in "ring level 0" on an Intel-based processor is part of the operating system, and everything else is not. If the user interface were in ring level 0, programs would be running with kernel permissions, and could thus take over the system without difficulty, since they would already be "in the kernel."

The user interface is not trusted, and so runs outside the kernel to allow the system to be more reliable.