Learn: The Fetch-Decode-Execute Cycle

Welcome!Today, we're going to learn all about the Fetch-Decode-Execute Cycle (FDE Cycle), a key process carried out by the CPU. This lesson is tailored to help you understand how computers process instructions step by step.

What is the Fetch-Decode-Execute Cycle?The Fetch-Decode-Execute Cycle is the process by which the CPU carries out instructions in a computer program. It involves fetching the instruction from memory, decoding it to understand what needs to be done, and executing the instruction.

Step 1: FetchDuring the Fetch stage, the CPU retrieves an instruction from memory. The Program Counter (PC) keeps track of the memory address of the next instruction to be fetched. The instruction is then stored in the Memory Address Register (MAR).

Step 2: DecodeOnce the CPU fetches the instruction, it moves to the Current Instruction Register (CIR). The Control Unit (CU) then reads the instruction, breaks it down, and determines what needs to be done. This is called the Decode stage.

Step 3: ExecuteIn the Execute stage, the decoded instruction is carried out. The Arithmetic Logic Unit (ALU) performs calculations, comparisons, or logical operations based on the instruction, and the result is stored in a register or memory.

How Registers Work in the FDE CycleRegisters are small, fast storage locations inside the CPU. Key registers include the Program Counter (PC), Memory Address Register (MAR), Memory Data Register (MDR), and Current Instruction Register (CIR). Each plays a specific role in the Fetch-Decode-Execute Cycle.

Clock Speed and CPU PerformanceThe clock speed of the CPU determines how many instructions it can process per second. A higher clock speed means faster processing. For example, a CPU with a clock speed of 3 GHz can process 3 billion cycles per second.

Review Time!Great work! You've learned about the Fetch-Decode-Execute Cycle, the roles of key CPU components, and how clock speed affects CPU performance. Let's test your understanding with a few questions.