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The Restaurant Order System
The Restaurant Order System
Think of a restaurant kitchen getting orders. First, the waiter fetches the order slip from the counter (gets the instruction from memory). Then, the head chef decodes it - "Table 5 wants pasta" becomes "boil water, cook pasta, add sauce" (Control Unit interprets the instruction). Finally, the sous chefs execute the tasks - actually making the dish (ALU does the work). This cycle repeats billions of times per second - fetch the next order, decode what it means, execute the steps, then immediately fetch the next order!
What does FDE stand for?: Fetch-Decode-Execute
Computer Science glossary
- What does FDE stand for?
- Fetch-Decode-Execute
Deep Dive: The Heartbeat of Computing
Every single thing your computer does goes through this cycle. Clicking a mouse? FDE cycle. Typing a letter? FDE cycle. Rendering a game frame? Millions of FDE cycles per second. This three-stage pattern is the fundamental rhythm of all modern computers.
Earn the mark scheme marks
Exam Tips - FDE Cycle
The FETCH sequence is a guaranteed 4-mark question! Learn this by heart:
- Line 1: "PC is copied to MAR" (1 mark)
- Line 2: "Address sent via Address Bus to memory" (1 mark)
- Line 3: "Instruction sent via Data Bus to MDR, then copied to CIR" (1 mark)
- Line 4: "PC is incremented to point to next instruction" (1 mark)
Common exam questions:
- "Describe the FETCH stage" → Use the 4 steps above, one per line
- "What happens in DECODE?" → Control Unit examines instruction in CIR, works out what operation to perform
- "When does PC increment?" → During FETCH (NOT execute!)
- "When does ACC change?" → During EXECUTE (when ALU completes calculation)
Common mistakes to avoid:
- Saying PC increments during EXECUTE - it's during FETCH!
- Missing the MAR and MDR registers in the FETCH sequence
- Forgetting to mention CIR (Current Instruction Register)
- Saying data changes during DECODE - nothing changes in DECODE!
Now try it yourself
Quiz · Question 1 of 16
What does FDE stand for in computer science?
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