One of the canards that’s regularly trotted out in discussions of ARM vs. x86 processors is the idea that ARM chips are intrinsically more power efficient thanks to fundamental differences in the ISA (instruction set architecture). A new research paper examines these claims using a variety of ARM cores as well as a Loongson MIPS microprocessor, Intel’s Atom and Sandy Bridge microarchitectures, and AMD’s Bobcat.
This paper is an updated version of one I’ve referenced in previous stories, but its methods and claims are worth investigating in more detail. ISA investigations are intrinsically difficult given that it’s effectively impossible to separate the theoretical efficiency of an architecture from the proficiency of its design team or the technical expertise of its manufacturer. Even products that seem identical can have important differences — ARM revised the Cortex-A9 core four different times and has released three updates to the Cortex-A15. Then you have the particulars of manufacturing — Intel, TSMC, Samsung, and GlobalFoundries aren’t carbon copies of each other and the CPU inside a Tegra K1 isn’t 100% identical to the Cortex-A15 inside a Samsung Exynos SoC.
That’s just the hardware side of the equation. Toss in compiler optimizations and library support and it’s even harder to write a definitive apples-to-apples comparison of any two architectures.
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