What is a fundamental requirement for the operation of a Graphical User Interface?

A fundamental requirement for the operation of a Graphical User Interface (GUI) is that an operator must give one command at a time. This principle aligns with how most GUIs are designed to work, allowing users to interact with the system in a sequential manner. In a typical GUI, a user will click on icons or buttons, make selections, or fill forms, and each action is processed individually before the user can proceed to the next command.

In many cases, while a GUI may offer features such as multitasking through tabs or windows, each command or action a user initiates must be completed or processed before the next can be executed within the same context. This sequential nature facilitates clarity and prevents confusion, ensuring that users can easily understand the flow of their interactions with the interface.

Other choices, such as giving multiple commands at once or automating tasks without any commands, do not accurately describe the basic operability of a GUI. In a typical GUI, the operator's actions are discrete, requiring a focused command before further interaction can take place.