Learn: The Fetch-Decode-Execute Cycle

Welcome!You've already learned about the importance of the CPU in a computer system. Today, we'll build on that by exploring how the CPU processes instructions using the fetch-decode-execute cycle.

What is the Fetch-Decode-Execute Cycle?The fetch-decode-execute cycle is the process the CPU uses to carry out instructions. It ensures that programs run by fetching instructions, interpreting them, and performing the required actions. This cycle happens millions or even billions of times per second!

Step 1: FetchDuring the fetch stage, the CPU retrieves the next instruction from memory. The Program Counter (PC) stores the address of the next instruction, and this address is passed to the Memory Address Register (MAR). The instruction is then fetched into the Memory Data Register (MDR).

Step 2: DecodeIn the decode stage, the CPU interprets the fetched instruction. The Control Unit (CU) is responsible for decoding the instruction to understand what needs to be done. For example, it determines whether the instruction is a calculation or a data movement.

Step 3: ExecuteIn the execute stage, the CPU carries out the instruction. If the instruction is a calculation, the Arithmetic Logic Unit (ALU) will perform the operation. If the instruction involves storing or retrieving data, it will access memory using the appropriate registers.

Registers in the CycleRegisters are small, fast storage locations inside the CPU. Important registers in the fetch-decode-execute cycle include the Memory Address Register (MAR), which holds the memory address, and the Memory Data Register (MDR), which temporarily stores the data or instruction fetched from memory.

The Importance of the Fetch-Decode-Execute CycleThis cycle is crucial because it allows the CPU to process instructions and perform tasks. Without it, computers wouldn’t be able to run software or respond to user inputs efficiently.

Review Time!Great work! You've learned about the fetch-decode-execute cycle and how the CPU processes instructions. Let's test your understanding with a few final questions.