Final answer:
The use of events to define functional requirements was first emphasized with real-time systems, which require event-driven programming to operate effectively and respond to events in a timely manner.
Step-by-step explanation:
The concept of using events to define functional requirements was first emphasized with real-time systems. These systems require event-driven programming, which is a key concept in defining how the system should react to external or internal events in a timely fashion. Functional requirements for a real-time system typically include detailed descriptions of the expected system behavior in response to specific events or inputs.
In contrast, business systems, operating systems, and batch systems use various methods for defining requirements, but the critical real-time response to events is a distinctive feature of real-time systems. This responsiveness is essential in applications such as embedded systems, telecommunication networks, and control systems where the timely processing of events is critical for the system's functionality and performance.