Which of the following is a feature of quality of service (QOS) requirements?

Quality of Service (QoS) requirements primarily address how well a system performs in terms of standards such as performance, reliability, and availability. When they define the system's operational behavior, they establish the expected criteria for responsiveness and how the system interacts with users and other systems under varying conditions. This understanding is crucial for ensuring that the system meets stakeholders' expectations and performs effectively in real-world scenarios.

On the other hand, while describing the interactions of system components is important for overall system design, it doesn’t specifically capture the essence of QoS, which is more about performance metrics rather than just component interaction. Focusing solely on user interface design neglects the broader aspects of QoS that extend beyond usability and aesthetics. Lastly, specifying hardware requirements addresses the physical resources needed for the system but does not inherently express how the system will perform its functions, which is the core of QoS evaluation.