Within the CPU (Central Processing Unit), which specific unit is responsible for performing arithmetic calculations and logical comparisons?

Introduction / Context:
The central processing unit (CPU) is often described as the brain of the computer. Inside the CPU, different sub units have different roles. One unit coordinates and controls the fetching and execution of instructions, while another unit performs the actual arithmetic operations and logical comparisons. Understanding this division of work is basic to computer architecture. This question asks which unit performs calculations and logical decisions inside the CPU.

Given Data / Assumptions:

• The focus is on parts of the CPU, not the entire computer.
• Options include the control unit, arithmetic and logic unit, both together, and a logic bus.
• Arithmetic calculations include addition, subtraction, multiplication, and division.
• Logical operations include comparison, AND, OR, and NOT operations on data.

Concept / Approach:
Inside the CPU, the control unit (CU) directs operations. It fetches instructions from memory, decodes them, and orchestrates when data moves between registers and when operations are applied. The arithmetic and logic unit (ALU) is the specialised circuitry that performs numerical calculations and logical operations on binary data. When an instruction requires addition, subtraction, or comparison, the CU instructs the ALU to perform the operation. A bus is simply a communication pathway and does not compute by itself. Thus, the ALU is the specific unit that performs calculations and logical decisions.

Step-by-Step Solution:
Step 1: Separate control from computation. The control unit manages the sequence of operations but does not perform the arithmetic itself. Step 2: Recall the definition of the ALU. The arithmetic and logic unit is designed to carry out arithmetic operations and logical comparisons on data. Step 3: Examine option B. Option B names the ALU explicitly and matches the textbook definition. Step 4: Evaluate option C. Although the CU and ALU work together, the actual calculations occur inside the ALU, not equally in both units. Step 5: Consider the logic bus. A bus transfers data and control signals but does not perform calculations.

Verification / Alternative check:
Computer organisation books break down the CPU into two main parts: the control unit and the arithmetic and logic unit. Diagrams show the ALU connected to registers and the control unit sending control signals. Descriptions state that the ALU performs operations like add, subtract, and logical AND, OR, NOT, while the control unit handles instruction sequencing. The term logic bus does not appear as a separate computing unit in standard diagrams. This evidence confirms that arithmetic and logical operations are performed in the ALU, making option B correct.

Why Other Options Are Wrong:
Option A (Control unit): The CU directs operations but does not perform the mathematical or logical calculations itself. Option C (Both the control unit and the arithmetic and logic unit equally): This overstates the role of the CU; only the ALU performs the actual calculations. Option D (The logic bus connecting components): A bus is a communication channel for data and addresses, not a computing unit.

Common Pitfalls:
Students sometimes answer control unit because it seems like the most important part of the CPU. They may think that controlling means doing everything. Others may choose both CU and ALU to recognise that the two units cooperate, but exam questions usually want the specific unit that executes arithmetic and logical operations. To avoid errors, memorise the roles: the control unit controls, the ALU calculates. Whenever the question emphasises calculations or comparisons, the ALU is the answer.

Final Answer:
The part of the CPU that performs calculations and logical comparisons is the arithmetic and logic unit (ALU).