A1.3 Operating systems and control systems

The drone becomes unresponsive because video streaming is consuming excessive CPU time, starving safety-critical processes like flight stabilization. This is a timing and prioritization problem in a safety-critical embedded system.

An RTOS (Real-Time Operating System) is specifically designed to ensure that time-critical tasks complete within guaranteed deadlines. It uses deterministic scheduling — critical processes like flight stabilization are always given CPU time before lower-priority tasks like video streaming.

A drone in flight is a safety-critical, time-sensitive system. Missing a deadline for flight stabilization could cause a crash. This matches the exact use case for an RTOS — embedded, real-time control where response time must be guaranteed and deterministic.

The correct answer is the RTOS option. It directly addresses the problem by ensuring critical processes are never starved of CPU time, regardless of what other processes are doing.

The question asks which OS type best prevents a safety-critical process from being starved by a lower-priority process in an embedded control system.

A general purpose OS (like Windows or macOS) aims for overall usability and throughput but provides non-deterministic response times — it cannot guarantee that flight stabilization will always execute on schedule. This option is incorrect.

A batch processing OS executes jobs in sequence without interactive real-time responses. This would be completely unsuitable for a drone, which requires simultaneous, concurrent, time-critical control processes.

A single-user OS restricts the number of user accounts, not the number of processes. It does nothing to address the problem of one process consuming too much CPU time and starving others.

The RTOS option is correct because it is specifically engineered to provide deterministic, deadline-guaranteed scheduling, making it the only suitable choice for safety-critical real-time systems like drone flight control.

The question tests the difference between sensors (input side) and actuators/output transducers (output side). Understanding which converts physical → electrical versus electrical → physical is essential.

A sensor detects a physical quantity from the environment and converts it into an electrical signal that the controller can process. In this case, the soil moisture sensor measures moisture (a physical quantity) and produces an electrical signal representing that value.

The soil moisture sensor performs physical → electrical conversion, which is the defining characteristic of an input sensor. It sits on the input side of the control loop, feeding data into the microcontroller.

The correct answer is "Input sensor, because it converts the physical quantity of soil moisture into an electrical signal for the controller." This precisely matches the definition of a sensor in a control system.

The question asks for the correct role and description of the soil moisture sensor in a closed-loop control system.

An output transducer converts electrical signals into physical actions (e.g., a motor or heater). A moisture sensor does not produce a physical action — it reads a physical state, so this is incorrect.

An actuator performs a physical action in response to the controller's decision. In this system, the water pump is the actuator — not the moisture sensor. This option confuses the sensor with the output component.

The controller (microcontroller) is the component that compares the sensor reading to the threshold and decides whether to activate the pump. The moisture sensor simply provides data — it does not make decisions.

The input sensor option is correct. It accurately describes the soil moisture sensor's role: converting a physical measurement into an electrical signal on the input side of the control loop.