Learn: The Fetch-Decode-Execute Cycle

Welcome!Building on what you've already learned about why the CPU is essential, this lesson will explore the Fetch-Decode-Execute Cycle. We'll learn what it is, why it's important, and how it works step by step. Let's get started!

What is the Fetch-Decode-Execute Cycle?The Fetch-Decode-Execute Cycle is the process by which the CPU carries out instructions. It is a continuous cycle that allows the computer to perform tasks, from simple calculations to running complex applications. Understanding this cycle is key to knowing how the CPU functions.

Step 1: FetchIn the fetch step, the CPU retrieves an instruction from memory. The Program Counter (PC) holds the memory address of the next instruction. This address is sent to the Memory Address Register (MAR), which locates the instruction in memory. The instruction is then copied into the Memory Data Register (MDR).

Step 2: DecodeIn the decode step, the CPU interprets the instruction. The Control Unit (CU) is responsible for decoding the instruction stored in the Memory Data Register (MDR). The CU determines what needs to happen and prepares the necessary components of the CPU for execution. This step ensures the CPU knows exactly what to do next.

Step 3: ExecuteIn the execute step, the CPU carries out the instruction. This might involve calculations by the Arithmetic Logic Unit (ALU), transferring data to or from memory, or changing the Program Counter to point to the next instruction. The execute step is where the CPU turns the decoded instructions into actions.

How Registers WorkRegisters are small, fast storage locations within the CPU. Key registers include the Program Counter (PC), the Memory Address Register (MAR), the Memory Data Register (MDR), and the Accumulator. Each register has a specific role in the fetch-decode-execute cycle.

Review Time!Great work! You've learned about the three steps of the Fetch-Decode-Execute Cycle and the roles of key components like registers. Let's test your understanding with some questions.

Well done!You've completed the lesson on the Fetch-Decode-Execute Cycle. Understanding this process is key to knowing how the CPU operates. Keep practising to reinforce your knowledge!