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is a longer CPU Pipeline better?

By harvardd ·
I understand that the classic Pentium chips have two pipelines. Each Pipeline has fives stages of executions.

What are the benefits of a 10 stage pipelines and 20 stage pipelines in the Pentium 4 chip? Can you explain what is a 20 stage pipeline?

Are there any references on 20 stage pipelines?

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is a longer CPU Pipeline better?

by TechKid In reply to is a longer CPU Pipeline ...

Apple used to have a great QuickTime movie on this. Basically, a longer pipeline doesn't necessarily mean 'better'. Hence the lack of performance on the P4's. A pipeline empties every so often based on the program it's running. While the pipeline isempty it is not processing, until it fills up again. Having more, shorter pipelines decreases this lag.

That's extremely basic but I hope you get the idea. An analogy I've heard is of a fast food restaurant. An Intel processor uses a 'drive up window' where as Apple uses a RISC processor or it's like going into the restaurant. Sure the drive up may be quicker but it can only serve one person at a time and has a longer line. Inside the restaurant there are multiple shorter lines and is often quicker. It's a weak one but hey... additionally, a process from one pipeline may depend on the result from another pipeline. Having shorter pipelines reduces the lag time between processes therefore decreasing the time one pipeline is waiting for another to finish processing.

Very difficult to sumarize pipelines in a paragraph. Hope it helped though

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is a longer CPU Pipeline better?

by harvardd In reply to is a longer CPU Pipeline ...

The question was auto-closed by TechRepublic

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is a longer CPU Pipeline better?

by PID In reply to is a longer CPU Pipeline ...

Hi

It depends, if the cpu can guess the instructions that are going to be performed correctly. As the program is running the cpu looks ahead x number of instructions to add to the pipeline. (Where x is the number of stages or lenth of the pipeline.) This makes the cpu faster because the instructions are ready waiting to be executed, so the CPU does not wait for instructions to be retieved from 'slow' ram.

But if the guess is wrong! Then the pipeline is flushed and the correct instuction is loaded into the begin of the pipe. If the pipe is 20 long you now waste +-21 cycles.(One to flush the pipe then one for each instruction load at the begining of the pipe and work it down to the CPU end.) So if the branch perdiction is not good and this happens a lot the through put of instructions could be slower that with out a pipeline.

AFAIK if you understand a 5 stage pipeline you cat guess at a 20 stage as the princapible is the same. but you can try this URL
www.arstechnica.com/cpu/3q99/k7_theory/k7-one-1.html

Cheers
Pierre

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is a longer CPU Pipeline better?

by harvardd In reply to is a longer CPU Pipeline ...

The question was auto-closed by TechRepublic

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is a longer CPU Pipeline better?

by harvardd In reply to is a longer CPU Pipeline ...

This question was auto closed due to inactivity

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