Over the last few years, chipmakers have relied more and more on integration to save energy, use less physical space, and increase performance in their products. It started with little things like the memory controller, but we have reached the point where almost every important chip in a computer can be combined into one do-everything piece of silicon called a "system-on-a-chip" (or SoC for short).
This trend isn't going anywhere, but a few high-end phones recently have been trying something a bit different to enable unique features—they've included one (or more) small, low-power, extremely specialized co-processors designed to support very specific features. Why do this instead of building those features into the SoC along with everything else? We'll look at the just-announced iPhone 5S and the recently released Moto X to explain why.
The M7 co-processor in the 5S and the pair of co-processors in the Moto X's "X8 Computing System" have one big thing in common: they're designed to do their thing when the phone is idle, or mostly idle. The M7 receives and processes data from the iPhone's various motion sensors, even when the phone is off and in your pocket, and one of the two co-processors in the Moto X is designed to show the low-power Active Notifications when the phone moves; the other is always listening for voice input.