macOS (formerly Mac OS X)

The modern operating system is now termed macOS, after an entire generation of OS X and its many variants (10.1, 10.2, and the current 10.4) having initially been given feline code names - Cheetah, Jaguar, Panther, , , these days turned into grander monikers like El Capitan, Sierra, etc.

It is essentially a current-day version of NeXTSTEP with the Aqua interface wrapped around it - that is to say, a BSD-like system running on top of the Mach microkernel.

The best currently available online reference to its internals is Amit Singh's What Is Mac OS X?, which I recommend heartily to anyone coming from mainstream systems like and BSD - it explains most of the rationale and heritage of in a exceptionally clear and well written fashion, and draws appropriate comparisons as it goes along.

Amit has also recently published a must-have book on , and made available a vastly extended version of its initial chapter covering 's precursors and history.

O'Reilly also has a great book for people coming to from other es called Mac OS X for Unix Geeks:

Tools:

Networking:

Essentials:

Unix:

Carbon/Cocoa:

Mach and Mach-O

Neat Stuff:

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