From the Introduction

MacOS Catalina is the 16th major version of Apple’s operating system. It’s got very little in common with the original Mac OS, the one that saw Apple through the 80s & 90s. Apple dumped that in 2001, when CEO Steve Jobs decided it was time for a change. Apple had spent too many years piling new features onto a software foundation originally poured in 1984. Programmers and customers complained of the “spaghetti code” the Mac OS had become.

So today, underneath macOS’s classy, shining desktop is Unix, the industrial-strength, rock-solid OS that drives many a website and university. It’s not new by any means; in fact, it’s decades old & has been polished by generations of programmers.

To find your way around macOS Catalina, you’re expected to use Apple’s online help system. As you’ll quickly discover, these help pages are tersely written, offer very little technical depth, lack useful examples, and provide no tutorials whatsoever.

The purpose of this book, then, is to serve as the manual that should have accompanied macOS—version 10.15 in particular. Whether you have an antique, hand-cranked 2012 iMac or a shiny new model, this is your guide.

If you’re a Mac veteran, on the other hand, keep your eye out for similar shaded boxes called “Power Users’ Clinic.” They offer more-technical tips, tricks, and shortcuts.