Athlon vs. Pentium

**JiM PolPot v.W.o.** · 01-20-2006, 05:54 AM

A good ol' throughput versus latency post...

Definitions:
Latency is how long is takes for something to happen.
Throughput is the amount of things happening per unit time.
Pipelines are the stages of logic that a processor uses to execute an instruction.

Intel has lower latency due to the increased clock speeds. However, AMD can achieve the same throughput as the Intel chips at a much lower clock speed. The reason for this is because the Intel chips have very long pipelines (between 20-32 stages). The longer pipelines allow instructions to be broken up into smaller chunks, which result in less propagation delay between registers, and therefore allow for a higher clock speed. However, the design of the Netburst architecture (which is used in the pentium 4) requires many stall states for dependencies between consecutive instructions. This is the tradeoff of making a pipeline longer. This means that although the clock is running at an extremely high rate, the processor is just sitting there doing nothing for many of those clock cycles. Overall, the AMD has a shorter pipeline and is better at avoiding stalls. They invested the chip's real estate in extra logic to avoid the stalls rather than extra logic for additional pipeline stages. The investment has paid off.

As far as the lower latency on the Intel chips, you do not care about this because individual instructions do not matter as far as the completion of your program is concerned. The only thing that matters here is throughput.

My recommendation is to go with the AMD chips because they are cheaper and get the same performance.

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01-20-2006, 05:54 AM	#3
JiM PolPot v.W.o. v.W.o. for LIFE Posts: 6,062	A good ol' throughput versus latency post... Definitions: Latency is how long is takes for something to happen. Throughput is the amount of things happening per unit time. Pipelines are the stages of logic that a processor uses to execute an instruction. Intel has lower latency due to the increased clock speeds. However, AMD can achieve the same throughput as the Intel chips at a much lower clock speed. The reason for this is because the Intel chips have very long pipelines (between 20-32 stages). The longer pipelines allow instructions to be broken up into smaller chunks, which result in less propagation delay between registers, and therefore allow for a higher clock speed. However, the design of the Netburst architecture (which is used in the pentium 4) requires many stall states for dependencies between consecutive instructions. This is the tradeoff of making a pipeline longer. This means that although the clock is running at an extremely high rate, the processor is just sitting there doing nothing for many of those clock cycles. Overall, the AMD has a shorter pipeline and is better at avoiding stalls. They invested the chip's real estate in extra logic to avoid the stalls rather than extra logic for additional pipeline stages. The investment has paid off. As far as the lower latency on the Intel chips, you do not care about this because individual instructions do not matter as far as the completion of your program is concerned. The only thing that matters here is throughput. My recommendation is to go with the AMD chips because they are cheaper and get the same performance.