A great document has been produced by Apple expelling what goes on within the entire software stack, it covers items like:
App Nap, this puts applications that you’re not using into a special low-power state.
Sandboxes, ensuring that processes are only allowed to perform a specific set of expected operations.
AirPlay letting you stream music throughout your entire house.
Auto Save, you no longer need to manually!
All the way down to
Apple LLVM compiler, The next-generation Apple compiler.
Well worth a read, as Apple say-
With millions of users—consumers, scientists, animators, developers, and system administrators—OS X is the most widely used UNIX® desktop operating system.
In addition, OS X is the only UNIX environment that natively runs Microsoft Office, Adobe Photoshop, and thousands of other consumer applications—all side by side with traditional command-line UNIX applications. Tight integration with hardware— from the sleek MacBook Air to the powerful Mac Pro—makes OS X the platform of choice for an emerging generation of power users.
This document explores the powerful industry standards and breakthrough innova- tions in the core technologies that power Apple’s industry-leading user experiences. We walk you through the entire software stack, from firmware and kernel to iCloud and developer tools, to help you understand the many things OS X does for you every time you use your Mac.
direct link here