Describe about fetch and execution cycle.

Introduction

The fetch and execute cycle, also known as the instruction cycle, is the basic operational process of a computer system. It is the process by which a computer retrieves a program instruction from its memory, determines what actions the instruction requires, and carries out those actions. This cycle is repeated continuously by the central processing unit (CPU), from bootup to when the system is shut down.

Detailed Description of Fetch Cycle

The fetch cycle is the first part of the instruction cycle. It involves retrieving an instruction from the program memory. The steps involved in the fetch cycle are as follows:

1. Program Counter (PC) holds the address of the instruction to be fetched: The PC is a register in the CPU that holds the address of the next instruction to be fetched from memory.

2. The instruction at the address is fetched from memory: The CPU sends the address from the PC to the memory unit, which reads the data stored at that address and sends it back to the CPU.

3. The PC is incremented to point to the next instruction: After the instruction is fetched, the PC is incremented by 1 to point to the address of the next instruction.

Detailed Description of Execution Cycle

The execution cycle is the second part of the instruction cycle. It involves executing the instruction that has been fetched. The steps involved in the execution cycle are as follows:

1. The Control Unit decodes the instruction: The Control Unit of the CPU decodes the fetched instruction to determine what operation needs to be performed.

2. The Control Unit coordinates the necessary data movement: Depending on the instruction, the Control Unit may need to fetch additional data from memory, or retrieve data from a register.

3. The Arithmetic Logic Unit (ALU) performs the operation: The ALU performs the actual operation on the data. This could be an arithmetic operation, such as addition or subtraction, or a logical operation, such as comparing two values.

4. The result is stored in the appropriate place: Depending on the instruction, the result of the operation may be stored in a specific register, or it may be written back to memory.

Difference between Fetch and Execution Cycle

Conclusion

The fetch and execute cycle is fundamental to the operation of any computer system. It is the process by which a computer carries out the instructions in a program, from simple arithmetic to complex tasks like rendering graphics or managing databases. Understanding this cycle is crucial to understanding how computers work at a fundamental level.

Summary

The fetch and execute cycle, also known as the instruction cycle, is the basic operational process of a computer system. It involves retrieving an instruction from memory (fetch cycle) and executing that instruction (execution cycle). The fetch cycle retrieves the instruction from memory using the program counter (PC) and increments the PC to point to the next instruction. The execution cycle decodes the instruction, coordinates data movement, performs the operation using the arithmetic logic unit (ALU), and stores the result. Understanding the fetch and execute cycle is crucial to understanding how computers work.

Analogy

The fetch and execute cycle can be compared to a chef following a recipe. The fetch cycle is like the chef reading the next step in the recipe, while the execution cycle is like the chef actually performing that step. Just as the chef repeats this process for each step in the recipe, the computer repeats the fetch and execute cycle for each instruction in a program.