The correct option is
D. Control unit.
Detailed Explanation
- Understanding the CPU Components:
- The Central Processing Unit (CPU) is the brain of the computer where most calculations take place. It consists of several components, including the Arithmetic Logic Unit (ALU), Control Unit (CU), and registers.
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The Control Unit is a critical component of the CPU that manages and coordinates the activities of the CPU and other components of the computer.
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Instruction Fetching and Decoding:
- When a program is executed, instructions are fetched from the primary memory (RAM) into the CPU. This process is managed by the Program Counter (PC), which keeps track of the address of the next instruction to be executed.
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Once an instruction is fetched into the CPU, it needs to be decoded so that the CPU can understand what action to perform. This is where the Control Unit comes into play.
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Role of the Control Unit:
- The Control Unit takes the fetched instruction and decodes it. This means it interprets the instruction and generates the necessary control signals to direct the operation of the ALU, memory, and input/output devices.
- The Control Unit essentially acts as a traffic controller, ensuring that the right operations are performed at the right time based on the decoded instruction.
Why Other Options Are Incorrect
- A. Primary Memory:
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Primary memory (or RAM) is where data and instructions are stored temporarily while the CPU processes them. It does not have the capability to decode instructions; it simply holds them until they are fetched by the CPU.
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B. Program Counter:
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The Program Counter is responsible for keeping track of the address of the next instruction to be executed. While it plays a crucial role in the instruction cycle, it does not decode instructions. Its function is to point to the next instruction, not to interpret it.
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C. ALU (Arithmetic Logic Unit):
- The ALU is responsible for performing arithmetic and logical operations (like addition, subtraction, AND, OR, etc.). It executes the operations specified by the decoded instructions but does not decode the instructions itself. The decoding is the responsibility of the Control Unit.
Summary of Key Points
- The Control Unit is responsible for decoding instructions fetched into the CPU.
- The Program Counter tracks the next instruction but does not decode it.
- Primary Memory stores instructions and data but does not perform decoding.
- The ALU executes operations based on decoded instructions but does not handle the decoding process.
Revision Summary
- The Control Unit decodes instructions in the CPU.
- The Program Counter tracks instruction addresses, not decoding.
- Primary Memory holds instructions temporarily.
- The ALU performs calculations based on decoded instructions.