The Complete FDE Cycle

Part of Fetch-Decode-Execute Cycle · Section 7 of 10

DiagramUnit: 3.4 Computer SystemsGCSE

This diagram covers The Complete FDE Cycle within Fetch-Decode-Execute Cycle for GCSE Computer Science. Revise Fetch-Decode-Execute Cycle in 3.4 Computer Systems for GCSE Computer Science with 16 exam-style questions and 12 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 7 of 10 in this topic. Focus on the labels, the relationships between parts, and the explanation that turns the diagram into an exam-ready answer.

The Complete FDE Cycle

The Fetch-Decode-Execute Cycle 1. FETCH PC → MAR Address Bus → Memory Data Bus → MDR MDR → CIR PC = PC + 1 2. DECODE Control Unit examines CIR Split into opcode + operand Determine operation type Prepare control signals (No register changes) 3. EXECUTE Perform operation: • ALU calculation • Data transfer • PC change Result → ACC Repeat billions of times per second! Example: Executing "ADD 5" instruction at address 100 FETCH: • PC holds 100 • 100 → MAR → Address Bus → Memory • "ADD 5" instruction → Data Bus → MDR • MDR → CIR (now holds "ADD 5") • PC increments: 100 → 101 DECODE: • CU reads "ADD 5" from CIR • Opcode: ADD (addition) • Operand: 5 (value to add) • CU: "Prepare ALU for addition" • (No register changes) EXECUTE: • ACC currently holds 8 • ALU performs: 8 + 5 • Result = 13 • 13 stored in ACC • Cycle complete!

Practice questions for Fetch-Decode-Execute Cycle

What does FDE stand for in computer science?

  • A. Find, Delete, Execute
  • B. Fetch, Decode, Execute
  • C. Fetch, Decode, Evaluate
  • D. Format, Decode, Execute
1 markfoundation

Describe the three stages of the FDE cycle.

3 marksstandard

Quick recall flashcards

What does FDE stand for?
Fetch-Decode-Execute
What are the three stages of the FDE cycle?
Fetch, Decode, Execute (repeats continuously)

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Stage 3: EXECUTE - "Do the Instruction"

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FDE Stage Comparison

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