ARM have an advantage because they are not as powerful as something like x86.
Back in the day of the Acorn RISC machine the ARM not only consumed far less power than x86 of the time but was much faster.
Things moved on of course. Intel went for maximum performance in your PC. With long pipelines, bigger caches all kind of speed ups that require ever more transistors and more power. ARM landed in mobile devices where saving battery power was the name of the game and raw performance was secondary.
So what is the situation today? Is there an Intel x86 based system, like the Edisson or whatever, that has performance and power consumption that matches the Pi 3 or other ARM systems?
Is there an Intel system that matches the likes of the STM32 F4 in performance and power consumption?
There is a fundamental rule here - at the same process node, for the same power consumption, it doesn't matter what the architecture is, the processor power with be roughly similar for similar die areas IF the implementation quality is similar (e.g. caching pipelining, prediction etc). Nowadays, the underlying micro-architecture implements the instruction set, for example X86 is not implemented directly, but over a micro-architecture, which makes it pretty much the same as ARM.
Of course, Intel use much smaller process nodes, and many more transistors, so they can perform much better, but also use more power. Remember, when it comes down to it, processors are mainly transistors, and transistors take similar levels of power whatever the architecture. So, a combination of die area and process node gives the total number of transistors. And that is what determines overall power and power consumption.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
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