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I'm not sure if this is a place to ask questions, but here it is: How can I compare ARM and x86 CPUs based on their specs, e.g. without actually testing them. R

• TillE 14y ago
  Look at benchmarks. It's not perfect, but that's the only reasonable way.
• Symmetry 14y ago
  No, different specific architectures can have more than an order of magnitude difference in performance per clock in ways that don't have anything to do with the instruction set used. In this case, the Pentium 2 is an out of order 2-wide superscalar architecture and so is the A9 ARM processor talked about in this article, but the ARM 11 in the RasberryPi is a 1-wide in order processor, which mostly accounts for the wide disparity in performance. You'd actually normally expect the difference to be larger, but ARM instructions are a bit more powerful than x86 instructions so you'll tend to need less of them[1]. But x86 is more efficiently encoded, so you only need the same number of bytes of instructions to accomplish the same task for each. The best way to compare different processors is by benchmarks. But remember to choose a benchmark that looks like what you're trying to do, because different architectures can excel in different situations. [1] x86 has the advantage of having combined load/store and operate instructions, but ARM has 3-operand instructions, twice the registers instruction predication, and a free barrel roll when using it's ALU. Changes to the x86 instruction set since the Pentium 2 make things more fair.