Fundamentally, what is a PC architecture, what is the difference between x64, x86, ARM, whatever else etc. and why do they offer different benefits or drawbacks or performances
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They are instruction sets. The set of all the instructions a CPU can execute.
Historically ARM and x86 had different design goals.
When the 8086 (the first of the x86 processors) was created memory was very expensive. Intel designed the instruction set where each instruction could perform multiple functions. For example, read a from memory, add to it, write back to memory. This reduced the size of programs, which saved memory.
ARM followed the RISC (Reduced Instruction Set Computer) design, as was fashionable at the time. This means each instruction performs only one function. For example, read from memory, add to it, and write back to memory takes 3 instructions. The idea is that the less complex circuitry of the simpler instructions would allow the CPU to be clocked higher and give better performance.
Historically ARM found success in embedded devices like smartphones and televisions, routers, etc. It’s not until very recently that they started showing up in PCs and servers.
The fact that ARM powers low-power devices has nothing to do with the instruction set itself. It’s just the niche that they happened to fill at the time.
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