1. PIPELINING Santosh Lakkaraju CS 147 Dr. Lee

2. Pipelining • What is it? • How does it work? • What are the benefits? • What could go wrong?

3. What is pipelining? Pipelining is a design feature that allows individual common processor tasks to run simultaneously, such as: FetchDecodeExecute

4. What is pipelining? Or, more specifically in modern computers, Instruction readDecodeOperand readExecuteOperand write

5. What is pipelining? • No more “one instruction at a time” processing • Processor works simultaneously on multiple instructions • The cycle time of the processor is reduced, thus increasing instruction issue-rate in most cases.

6. How does pipelining work? • First instruction is fetched from memory

7. How does pipelining work? • First instruction is fetched from memory • First instruction is decoded;second instruction is fetched

8. How does pipelining work? • First instruction is fetched from memory • First instruction is decoded;second instruction is fetched • First instruction’s operands are fetched;second instruction is decoded;third instruction is fetched

9. How does pipelining work? • First instruction is fetched from memory • First instruction is decoded;second instruction is fetched • First instruction’s operands are fetched;second instruction is decoded;third instruction is fetched • And on, and on, and on…

10. How does pipelining work? • Because each instruction demands one stage of the processor, the maximum number of simultaneous instructions is the number of stages in the processor

11. How does pipelining work? A short animation of simple processor routines

49. How does pipelining work? A short(er) animation of pipelined processor routines