Which of the following is a common disadvantage or limitation of using general purpose microprocessor based systems?

Introduction / Context:
Microprocessors provide flexibility and programmability, which are major advantages. However, this flexibility also introduces some disadvantages compared to fixed function hardware or dedicated logic circuits. Understanding these trade offs helps engineers choose the right solution for each application. This question asks you to identify a realistic disadvantage of general purpose microprocessor based systems.

Given Data / Assumptions:

• A general purpose microprocessor needs external memory, clock circuitry, and input or output interfaces.
• Software must be developed and maintained for the system to perform useful tasks.
• Some tasks can be implemented using simpler dedicated hardware.

Concept / Approach:
Because microprocessors are programmable, they can support many applications on the same hardware. This flexibility costs resources. A microprocessor based design needs power for the CPU and its support chips, non volatile memory to store the program, and often an operating system. For simple functions such as turning a motor on and off or generating a fixed timing signal, a dedicated logic circuit or small microcontroller may be more cost effective, consume less power, and require less board space. Therefore, complexity and resource usage can be seen as disadvantages when a simple fixed function solution would be sufficient.

Step-by-Step Solution:
Step 1: List the overheads of using a general purpose microprocessor, including external memory, power supply requirements, and software development.Step 2: Compare this with fixed function logic, which can sometimes perform simple tasks with minimal hardware.Step 3: Recognize that for very simple control tasks, a full microprocessor system can be overkill.Step 4: Select the option that describes this disadvantage in terms of complexity, power usage, and cost.

Verification / Alternative check:
Design examples help verify this reasoning. A basic electronic timer could be implemented with a handful of logic gates and a timer integrated circuit, consuming little power and costing very little. Building the same timer around a full microprocessor, external memory, and support components would greatly increase cost and design time without providing benefits for such a simple task. This comparison supports the idea that complexity and overhead are valid disadvantages.

Why Other Options Are Wrong:
Option B: Claims that microprocessors can only run a program once, which is false. They are designed to execute many programs repeatedly.Option C: States that microprocessors cannot interface with external memory or devices, which is the opposite of their intended design.Option D: Suggests that microprocessors work only with analog signals, but they are digital devices that process digital data and instructions.

Common Pitfalls:
Sometimes learners focus only on the strengths of microprocessors and forget that adding a microprocessor to every problem is not always optimal. Another mistake is to equate microprocessors and microcontrollers; microcontrollers address some of these disadvantages by integrating memory and peripherals, making them more suitable for simple embedded control tasks. Understanding when a microprocessor system is excessive helps in making better design decisions.

Final Answer:
The correct answer is They require supporting hardware and software and therefore can be more complex, power hungry, and expensive than fixed function hardware for very simple tasks.