Pipelining (OCR A Level Computer Science)
Revision Note
Written by: Jamie Wood
Reviewed by: James Woodhouse
Pipelining
What is Pipelining?
Pipelining is the process of carrying out multiple instructions concurrently
Each instruction will be at a different stage of the fetch-decode-execute cycle
One instruction can be fetched while the previous one is being decoded and the one before is being executed
In the case of a branch, the pipeline is flushed
This table shows which stage each instruction is at during each step:
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|
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|---|---|---|---|
Step 1 | Instruction A |
|
|
Step 2 | Instruction B | Instruction A |
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Step 3 | Instruction C | Instruction B | Instruction A |
Step 4 | Instruction D | Instruction C | Instruction B |
While one instruction is being executed, the next instruction will be decoded and the following instruction will be fetched
How Does Pipelining Improve Processor Performance?
Pipelining reduces latency
The CPU is not idle while waiting for the next instruction which increases the speed of execution
The next instruction is fetched while the current one is decoded/executed
All parts of the processor can be used at any instance in time
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