What identifies that a computer has successfully completed its boot process?

The successful completion of the boot process is indicated by the appearance of the operating system interface. During booting, the computer undergoes several diagnostic checks and loads essential system files, ultimately transitioning to an interface that allows the user to interact with the operating system. This interface can be a graphical desktop environment or a command-line interface, depending on the OS being used.

When the interface appears, it signifies that the operating system has been loaded into memory and is ready for user input, marking the end of the boot process. This is a clear signal that the hardware has initialized correctly, and all necessary drivers are functioning, which enables the user to operate the computer effectively.

In contrast, a black screen indicates that the boot process has not progressed to the point of loading the operating system. The power supply light turning off or the CPU fan stopping could occur at various points during operation and do not specifically denote that the boot process was completed successfully or that the system is fully operational.