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Learn: The Fetch-Decode-Execute Cycle
OCR GCSE J277 Computer Science specification
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Welcome!Building on what you've already learned about why the CPU is essential, today we'll explore how it processes instructions using 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 constantly while the computer is running, ensuring programs and tasks are completed correctly.
Key Components InvolvedThe cycle relies on the Program Counter (PC), Memory Address Register (MAR), Memory Data Register (MDR), and Accumulator. These work together to fetch instructions, decode them, and execute them.
Quick check: What is the main purpose of the Fetch-Decode-Execute Cycle?
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Step 1: FetchDuring the Fetch stage, the CPU retrieves the next instruction from memory. The Program Counter contains the address of the instruction, which is passed to the Memory Address Register (MAR). The instruction is then copied to the Memory Data Register (MDR).
During the fetch stage, the {{blank0}} contains the address of the next instruction, which is sent to the {{blank1}}.
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Step 2: DecodeIn the Decode stage, the CPU interprets the instruction. The Control Unit reads the instruction from the Memory Data Register (MDR) and decides what needs to happen.
What role does the Control Unit play during the decode stage?
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Step 3: ExecuteIn the Execute stage, the CPU carries out the instruction. This might involve calculations performed by the Arithmetic Logic Unit (ALU), storing data, or interacting with input/output devices.
Match the items on the left with their correct pairs on the right
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Review Time!Great work! You've learned about the Fetch-Decode-Execute Cycle and its steps. Now let's test your understanding with a few questions.
Which of the following are part of the Fetch-Decode-Execute Cycle? (Select all that apply)
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The {{blank0}} performs calculations during the execute stage, while the {{blank1}} interprets instructions.
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What happens during the fetch stage?
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