Learn: The Fetch-Decode-Execute Cycle

Welcome!Welcome back! Previously, you learned about why the CPU is essential for a computer. Today, we're building on that knowledge to explore the Fetch-Decode-Execute Cycle, which is how the CPU processes instructions.

What is the Fetch-Decode-Execute Cycle?The Fetch-Decode-Execute Cycle is the process the CPU uses to run instructions. It happens billions of times per second and ensures your computer operates smoothly. This cycle has three main steps: fetching the instruction, decoding it, and then executing it.

Step 1: FetchDuring the fetch part of the cycle, the CPU retrieves the next instruction from memory. The Program Counter (PC) stores the address of the next instruction, which is then placed into the Memory Address Register (MAR). The data at that address is transferred to the Memory Data Register (MDR).

Step 2: DecodeIn the decode step, the CPU examines the instruction to understand what needs to be done. The Control Unit (CU) interprets the instruction and prepares the CPU for the execution step. It identifies which components, such as the Arithmetic Logic Unit (ALU), will be used.

Step 3: ExecuteThe final step is execution. The instruction is carried out, which could involve calculations, moving data, or interacting with input/output devices. The Arithmetic Logic Unit (ALU) performs calculations and logical operations as needed, and the result is stored in the Accumulator.

Putting It All TogetherThe three steps — fetch, decode, and execute — form a continuous cycle. The CPU repeats this process for every instruction, ensuring the computer can perform complex tasks quickly and efficiently.

Review Time!Great work! You've learned about the key steps in the fetch-decode-execute cycle and the roles of important CPU components. Now let's test your understanding with a few questions.