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The decline of Intel..
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This is a most excellent place for technology news and articles.
It's not just node, it's also the design. If I remember properly, ARM has constant instruction length which helps a lot with caching. Anyway, Apple's M CPUs are still way better when it comes to perf/power ratio.
Yes, it's certainly more complicated than that, but the lithography is a huge part since they can cram more transistors into a smaller area, which is critical for power savings.
I highly doubt instruction decoding is a significant factor, but I'd love to be proven wrong. If you know of a good writeup about it, I'd love to read it.
Here, I've found an article. M CPUs are also much more integrated, like a SoC, which gives them further performance/power advantages sacrificing extensibility.