Learn: The Fetch-Decode-Execute Cycle

Welcome!Welcome, Year 10 student! Today, we'll explore how the Fetch-Decode-Execute Cycle works in a CPU. This is a key process in computer systems, so let's dive in step by step!

What is the Fetch-Decode-Execute Cycle?It’s the process a CPU follows to carry out instructions. It ensures that the computer understands and executes commands in the correct order. This cycle is fundamental to how all computers work.

Step 1: FetchThe Fetch step involves retrieving an instruction from memory. The Program Counter (PC) stores the address of the next instruction, and the Memory Address Register (MAR) sends this address to memory. The instruction is then copied into the Memory Data Register (MDR).

Step 2: DecodeIn the Decode step, the CPU interprets the instruction. The Current Instruction Register (CIR) holds the instruction, and the Control Unit (CU) breaks it down into actions the CPU can perform. This step ensures the CPU knows what to do next.

Step 3: ExecuteIn the Execute step, the CPU carries out the decoded instruction. This could involve calculations in the Arithmetic Logic Unit (ALU), accessing memory, or updating registers. The CPU completes the task before moving to the next instruction.

Registers and Their RolesRegisters are small storage locations inside the CPU. Key registers in the Fetch-Decode-Execute Cycle include the Program Counter (PC), Memory Address Register (MAR), Memory Data Register (MDR), Current Instruction Register (CIR), and Accumulator (ACC). Each plays a role in processing instructions efficiently.

Review Time!Great work! You've learned about the Fetch-Decode-Execute Cycle and the roles of key registers. Let’s test your understanding with a few final questions.