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This is not a production question, just something that I've been thinking about.

When speccing out CPUs I know the general rule is a faster clock speed will make a core run faster and the greater number of cores you have the more you can do in parallel. However what makes a "newer" CPU generally faster than an older CPU other than these two things?

For example:

  • There is a noticeable difference between an older i5 and a newer i5 despite having the same number of cores and around the same GHz.

  • My current dual core i5 running at 2.5 (I believe) GHz would surely blow a Pentium 4 out of the water, despite the Pentium running at > 3GHz. I'm sure I could blow a dual core server from 2004 out of the water as well just to make things fair core-wise. I have never done any formal benchmarking, these are just educated guesses.

What are some things to look for when speccing out CPUs?

marked as duplicate by bwDraco, Art Gertner, Kevin Panko, Nifle, mdpc Apr 27 '15 at 21:03

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  • it seems like you're asking two different questions here. are you asking what makes newer CPUs faster than older ones or what to look for in new CPUs? – nc4pk May 16 '13 at 21:59
  • Don't forget larger and faster cache memory and fast main memory. There is also the motherboard chipset to consider. – Matt H May 16 '13 at 22:51
  • "specing out CPUs" is what benchmarks are for. Unfortunately, it is difficult to find good benchmark results--SPEC CPU is probably the best available for "workstation" workloads--because many benchmarks are broken or have weak reporting rules. Applying benchmark results to estimate performance for one's own workload is a difficult art. – Paul A. Clayton May 17 '13 at 12:11


A CPU at 3.0Ghz means that the CPU is doing 3 billion somethings per second. As computer architectures grow more efficient, they are able to do more with each clock cycle (the something).

I haven't kept entirely up to date, but back when the Pentiums 4's were hot stuff, the reason comparable AMD processors had a lower clock rate was because they did more per clock cycle than the P4. The trade off is a clock cycle on an AMD processor took longer.

Some processors can execute multiple instructions in a single clock cycle. Some processors take multiple clock cycles to execute a single instruction. Many processors uses a technique called pipelining, which allows them to have instructions that take multiple clock cycles to execute, but still manage to execute roughly 1 instruction per clock cycle.

  • But how can you actually spec that out, numbers wise? I know an i5 is better than a P4, but I don't see any numbers why. – omgtestadsfasdf May 16 '13 at 22:00
  • Part of the problem is you can't, at least not in a general sense. At best you can pick a metric - you'll often see FLOPS, or floating-point operations per second as a general idea of raw computing power, but that translates badly to real-world scenarios outside of academic math / numbers crunching, and so isn't really useful. Bitcoining mining is concerned about hashing speed, so you'll find those measured in hashes/second. FLOPS are meaningless for that. You have to design the metric around what you're doing, not the other way around. – Darth Android May 16 '13 at 22:04

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