Final answer:
Direct I/O occurs with polling when a program actively checks the status of a device. The separation of mechanism from policy allows for flexibility and modularity in operating systems design.
Step-by-step explanation:
Direct I/O occurs with polling when a program actively checks the status of a device to determine if it is ready for input/output operations. This is done by using a loop that repeatedly checks the device status.
The separation of mechanism from policy is a desired option in operating systems design because it allows for flexibility and modularity. By separating the mechanism, which is the implementation details of how a certain feature or service is carried out, from the policy, which is the decision-making or control aspect of that feature or service, the operating system becomes more adaptable to different needs and can be easily updated or replaced.