Final answer:
The host signals the controller to execute a command by setting the command-ready bit, which is key for synchronized operation between them.
Step-by-step explanation:
The host sets the command-ready bit when a command is available for the controller to execute. In the context of computer hardware and communications, a host is a computer or other device that communicates with peripherals or other devices—think of it as the main conductor of operations that instructs other components or devices on what to execute. The controller, on the other hand, is often a separate hardware or software component that carries out the commands or operations directed by the host. By setting the command-ready bit, the host signals to the controller that there is a task ready to be executed, enabling synchronous operation between the host and the controller.