Stage 3: EXECUTE - "Do the Instruction"
Part of Fetch-Decode-Execute Cycle — GCSE Computer Science
This key facts covers Stage 3: EXECUTE - "Do the Instruction" within Fetch-Decode-Execute Cycle for GCSE Computer Science. Revise Fetch-Decode-Execute Cycle in Systems Architecture for GCSE Computer Science with 15 exam-style questions and 12 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 6 of 9 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 6 of 9
Practice
15 questions
Recall
12 flashcards
Stage 3: EXECUTE - "Do the Instruction"
Purpose: Carry out the actual operation specified by the instruction
What Happens Depends on Instruction Type:
Arithmetic/Logic Operation (e.g., ADD, SUBTRACT, AND):
- The ALU performs the calculation or logic operation
- The result is stored in the Accumulator (ACC)
- Example: ADD 5 → ALU adds 5 to current ACC value → new total goes to ACC
Data Transfer (e.g., LOAD, STORE):
- LOAD: Data is copied from memory to a register (usually ACC)
- STORE: Data is copied from a register to memory
- Example: LOAD 200 → fetch data from memory address 200 → copy to ACC
Control Flow (e.g., JUMP, BRANCH, CALL):
- The PC is changed to a different address (not just +1)
- This allows loops, IF statements, and function calls
- Example: JUMP 100 → PC is set to 100 → next FETCH will get instruction from address 100
Different instructions take different amounts of time: A simple ADD might take 1 clock cycle, but a MULTIPLY might take several cycles.