The central processing unit (CPU) of a computer mainly consists of a combination of which two logical units?

Introduction / Context:
The central processing unit (CPU) is often called the brain of the computer because it performs calculations and directs operations. Inside the CPU, there are distinct logical components that work together to execute instructions. Understanding which parts form the CPU helps you interpret textbook diagrams and exam questions about computer architecture. This question asks which two main logical units typically make up the CPU.

Given Data / Assumptions:

• The system is a general purpose digital computer.
• We are using the classic model that separates processing into control and arithmetic/logic functions.
• Options combine the Control Unit with different other units such as output, storage, and arithmetic.
• We assume standard terminology from computer fundamentals courses.

Concept / Approach:
In the classical von Neumann architecture, the CPU has two main parts: the Arithmetic Logic Unit (ALU) and the Control Unit (CU). The ALU performs arithmetic operations such as addition and subtraction, as well as logical operations such as AND, OR, and comparisons. The Control Unit orchestrates the fetching, decoding, and execution of instructions, sending control signals to the ALU, registers, and memory. Input and output units are separate parts of the system, and main storage (memory) is also considered outside the CPU, even though it works closely with it. Therefore, the correct combination is ALU and CU.

Step-by-Step Solution:
Step 1: Recall that the ALU is responsible for arithmetic and logical operations. Step 2: Recall that the Control Unit manages the instruction cycle and coordinates the activities of the CPU. Step 3: Recognise that both of these units are implemented inside the processor chip. Step 4: Note that the Output Unit includes devices like monitors and printers, which are not part of the CPU itself. Step 5: Note that the Storage or Memory Unit, while closely connected, is usually treated as a separate main memory component. Step 6: Choose the option that names the Arithmetic Logic Unit and the Control Unit together.

Verification / Alternative check:
Computer fundamentals books frequently present block diagrams of a computer system. These diagrams show the CPU box split into two parts: the ALU and the Control Unit. Input devices, output devices, and main memory are drawn as separate boxes connected to the CPU. This visual representation confirms that the two principal units inside the CPU are the ALU and the CU, not the combinations listed in the other options.

Why Other Options Are Wrong:
Control Unit and Output Unit: Output units are external devices, not core CPU components. Control Unit and Main Storage Unit: Main storage (RAM) is separate from the CPU, so this combination does not define the CPU. Arithmetic Logic Unit and Input Unit: The Input Unit consists of devices like keyboards and mice; it is not part of the CPU.

Common Pitfalls:
Students sometimes confuse the overall system unit (the computer case) with the CPU itself. The case may contain drives, ports, and other hardware, but the CPU is the actual processor chip that houses the ALU and CU. Remembering this distinction helps you answer questions that ask specifically about the internal structure of the CPU rather than the whole computer system.

Final Answer:
The CPU mainly consists of the Arithmetic Logic Unit (ALU) and the Control Unit (CU).