Learn: The Fetch-Decode-Execute Cycle

Welcome!Great to see you back! You've already learned about why the CPU is essential. Now, let's dive into how it works by exploring 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 happens billions of times per second and is essential for every task the computer performs. This cycle involves fetching an instruction, understanding it, and then executing it.

Step 1: FetchIn the fetch stage, the CPU retrieves the next instruction from the main memory (RAM). The Memory Address Register (MAR) holds the memory address of the instruction, and the Memory Data Register (MDR) temporarily stores the data fetched from that address.

Step 2: DecodeOnce the instruction is fetched, it is sent to the Control Unit (CU). The CU deciphers or decodes the instruction to understand what needs to be done. It identifies the operation required and the data needed for it.

Step 3: ExecuteIn the execute stage, the CPU carries out the instruction. This might involve performing a calculation in the ALU (Arithmetic Logic Unit), transferring data, or interacting with input/output devices. The result is stored in the Accumulator or sent to other parts of the system.

How Registers Work TogetherRegisters are tiny, fast storage locations inside the CPU. The Program Counter (PC) keeps track of the memory address of the next instruction. The instruction is fetched to the MDR, decoded by the CU, and executed. The cycle then repeats for the next instruction.

Review Time!Well done! You've learned about the key stages of the fetch-decode-execute cycle and the roles of the registers. Let's test your knowledge with some questions.