5.1.4 Instruction Cycle (Fetch, Decode, Execute, Store)

Computers, no matter how complex the programs they run, operate by repeating a very basic set of steps over and over again, billions of times per second. This fundamental sequence is called the Instruction Cycle, often referred to as the Fetch-Decode-Execute Cycle. It's the core process the CPU follows to carry out every single command in a program.

Imagine a chef following a recipe:

Fetch: First, the CPU goes to the computer's memory (like looking at a page in the recipe book) and retrieves the next instruction it needs to follow. It also figures out where the next instruction will be for the future.
Decode: Once the CPU has the instruction, it needs to understand what it means. This is like the chef reading the line "add two cups of flour" and understanding that "add" means to combine and "flour" is an ingredient. The Control Unit (CU) does this job, translating the instruction into specific commands for other CPU components, like the ALU.
Execute: This is where the actual work happens! The CPU performs the action that the instruction commanded. If the instruction was "add two numbers," the ALU would perform the addition. If it was "move data from one place to another," the CPU would manage that transfer. This step involves different parts of the CPU working together based on the decoded instruction.
Store (or Write Back): After the instruction has been executed, if there's a result (like the answer to an addition problem, or a piece of data that's been modified), that result needs to be saved somewhere. This result is usually stored back into a register or into the computer's main memory. This is like the chef noting down a measurement or placing a mixed ingredient back into a bowl.

This entire cycle happens incredibly quickly and continuously. The CPU constantly repeats these four steps for every single instruction in every program you run, making your computer the powerful and fast machine it is.

Bibliography for 5.1.4 Instruction Cycle (Fetch, Decode, Execute, Store)

Instruction Cycle Overview:
- Medium. "Understanding the CPU Instruction Cycle." Medium.com, https://medium.com/@ckekula/the-structure-of-a-processor-f851c32476ff
- GeeksforGeeks. "Instruction Cycle | Set 1 (Introduction)." GeeksforGeeks.org, https://www.geeksforgeeks.org/computer-organization-architecture/different-instruction-cycles/