It's no longer hard to find 64-bit processors in smartphones. In smartwatches, though, they're still a rarity -- and ARM wants to change that with its new Cortex-A35 processor design. The architecture promises the most energy-efficient 64-bit mobile chips yet, sipping 32 percent less power than the mid-range A53 even as it outruns the Cortex-A7 it's meant to replace (6 to 40 percent faster). It's extremely scalable, too. You can build full-fledged quad-core chips for entry-level smartphones, but you can also strip things back to make tiny chips for watches and activity trackers.