Learn: The Fetch-Decode-Execute Cycle

Welcome!Building on what you've already learned about why the CPU is essential, we're now going to explore how it processes instructions using the fetch-decode-execute cycle.This lesson will help you understand the steps the CPU follows to execute tasks and how different components work together.

What is the Fetch-Decode-Execute Cycle?The fetch-decode-execute cycle is the process the CPU uses to run instructions. It happens repeatedly and quickly, enabling the computer to function.It consists of three main stages: fetch (getting the instruction), decode (understanding it), and execute (carrying it out).

Step 1: FetchDuring the fetch stage, the CPU retrieves an instruction from memory. The Program Counter (PC) holds the address of the next instruction. The address is sent to the Memory Address Register (MAR), which accesses the location in memory.Then the instruction is copied into the Memory Data Register (MDR). The PC is updated to point to the next instruction.

Step 2: DecodeIn the decode stage, the CPU interprets the instruction. The Control Unit (CU) reads the data from the Memory Data Register (MDR) and determines what operation needs to be performed.This step ensures the CPU understands the instruction before proceeding to execute it.

Step 3: ExecuteIn the execute stage, the CPU carries out the instruction. This could involve calculations by the Arithmetic Logic Unit (ALU), moving data between registers, or interacting with input/output devices.The Accumulator is often used to store the result of calculations performed by the ALU.

Review Time!Great work! You've learned about the three steps of the fetch-decode-execute cycle and the roles of key components. Let's test your understanding with a few review questions.