In conceiving a feasible solution to running third-party apps in the extremely constrained power environment of the Apple Watch, Apple has come up with a rather peculiar yet familiar idea.
Initially, any third-party app processing will be offloaded to an iPhone in your pocket until the Cupertino firm begins accepting fully native Watch apps late next year.
Such an approach leaves only the app’s storyboards and user interface resources running directly on the Watch, with everything else happening on an iPhone.
The only exception that proves the rule are Apple’s stock apps which get executed on the Watch itself. In addition to acting as a viewport for third-party apps running on na iPhone, the Watch also manages Notifications and Glances and performs other lightweight housekeeping operations that don’t tax the battery much.