Learn: Fetch–Decode–Execute Cycle

Welcome!Today we'll explore the Fetch–Decode–Execute cycle, an essential process for how a computer's CPU operates. This lesson is tailored to help you understand it step by step!

What is the Fetch–Decode–Execute Cycle?The Fetch–Decode–Execute cycle is the process by which a CPU retrieves, interprets, and performs instructions from memory. It is a fundamental part of how computers function, enabling them to run software and complete tasks efficiently.

Step 1: FetchDuring the Fetch phase, the CPU retrieves the next instruction from memory. The Program Counter (PC) stores the memory address of this instruction, while the Memory Address Register (MAR) sends the address to memory. The instruction is then copied into the Memory Data Register (MDR).

Step 2: DecodeIn the Decode phase, the CPU interprets the instruction. The Current Instruction Register (CIR) holds the instruction, while the Control Unit deciphers what needs to be done, breaking it into smaller operations.

Step 3: ExecuteIn the Execute phase, the CPU performs the decoded instruction. This could involve calculations by the Arithmetic Logic Unit (ALU), transferring data, or interacting with hardware components. The output is stored or used immediately.

Registers and BusesThe CPU uses registers (small storage areas) and buses (communication pathways) to carry out the Fetch–Decode–Execute cycle. Key registers include the Program Counter (PC), Memory Address Register (MAR), Memory Data Register (MDR), and Current Instruction Register (CIR).

Review Time!Great work! You've learned about the Fetch–Decode–Execute cycle and key CPU components. Now let's test your understanding with a few final questions.