How many periods of pipeline does an Intel Pentium Pro have?

Question

At school we learned about the Intel Pentium processor. I read somewhere that the Intel Pentium was the first superscalar processor and had five periods of pipeline. My question leads to the Pentium Pro.

I read somewhere that the Pentium Pro has three Arithmetic Logic Units + a Floating Point Unit and all of these units have 14 periods of pipeline (three instructions per one tact). However I read elsewhere that it only has five periods of pipeline like the Pentium. I don't know which is true.

How many periods of pipeline does an Intel Pentium Pro have?

Answer 1

The Pentium was the first x86 processor that was superscalar, but it was far from being the first superscalar processor. The Pentium wasn't even the first Intel superscalar processor (that was the i960). See http://en.wikipedia.org/wiki/Superscalar for history.

Superscalar processors have multiple pipelines and these tend to have different lengths, so I'm not sure there's a simple answer to your question. Execution units tend to each have their own processing pipeline and then there is usually a common fetch/decode/despatch pipeline which feeds the various execution unit pipelines.

Answer 2

Ars Technica has a couple of good articles on the history of the Pentium architecture.

• Part 1
• Part 2

Answer 3

You might want to check out some of the pdf's available here http://www.agner.org/optimize/