ARM's N-series cores are targeted at a somewhat lower performance point than top line x86 cores. That saves a bunch of transistors since there's a lot of dimin

ARM's N-series cores are targeted at a somewhat lower performance point than top line x86 cores. That saves a bunch of transistors since there's a lot of diminishing returns. There's also design compromises not being made in order to hit clock speeds that server parts never try to hit anyways. Not having to decode complicated x86 instructions but simple RISC ones is also a small advantage, somewhere on the order of 5% power savings. Also, x86 backwards compatibility and SMT don't cost much in terms of power or transistors but both have large costs in of verification work.