Question

Which component of the central processing unit is primarily responsible for fetching, decoding and executing instructions?

• A. Arithmetic Logic Unit (ALU)
• B. Control Unit (CU)
• C. Cache Memory
• D. Registers

Hint:

Remember: ALU performs calculations, Registers store temporary data, Cache speeds up access, while the Control Unit manages the Fetch--Decode--Execute cycle.

Answer 1

The Correct Option is B

Concept: The Central Processing Unit (CPU) is often called the brain of a computer because it performs all major processing operations. The CPU consists of several important components such as the Control Unit (CU), Arithmetic Logic Unit (ALU), registers, and cache memory. Among these components, the Control Unit acts as the coordinator of all operations. It fetches instructions from memory, decodes them to determine the required operation, and directs other components to execute the instructions properly. The basic instruction cycle of a CPU consists of: \[ \text{Fetch} \rightarrow \text{Decode} \rightarrow \text{Execute} \] The Control Unit manages this entire sequence and ensures smooth communication between the processor, memory, and input-output devices.

Step 1: Understanding the role of the Arithmetic Logic Unit (ALU).
The Arithmetic Logic Unit performs arithmetic operations such as: \[ +,\;-,\;\times,\;\div \] and logical operations such as: \[ AND,\; OR,\; NOT,\; XOR \] Although the ALU performs calculations, it does not control the execution of instructions. Therefore, \[ \text{ALU} \neq \text{Fetch and Decode Unit} \] Hence, Option (A) is incorrect.

Step 2: Understanding the role of the Control Unit (CU).
The Control Unit is responsible for:
• Fetching instructions from memory.
• Decoding instructions.
• Sending control signals to different components.
• Coordinating execution of operations. Thus, the Control Unit supervises the complete instruction cycle. \[ \boxed{\text{Control Unit } \Rightarrow \text{Fetch + Decode + Control Execution}} \] Hence, Option (B) is correct.

Step 3: Examining Cache Memory.
Cache memory is a high-speed memory used to store frequently accessed data and instructions. Its purpose is to reduce access time and improve performance. It does not decode or execute instructions. Therefore, Option (C) is incorrect.

Step 4: Examining Registers.
Registers are small storage locations inside the CPU that temporarily hold data and instructions. Examples include:
• Program Counter (PC)
• Instruction Register (IR)
• Accumulator Registers assist processing but do not control the instruction cycle. Therefore, Option (D) is incorrect. Final Conclusion: The component responsible for fetching, decoding, and controlling the execution of instructions is the Control Unit. \[ \boxed{\text{Control Unit (CU)}} \] Hence, the correct answer is: \[ \boxed{\text{(B) Control Unit (CU)}} \]