|Much ado about Mach
Everyone likes to hate Mach, and even moreso if they don't know anything about it. But Mach haters never seem to mention OSF/1, renamed Digital Unix, and later Tru64.
The only other Unix that was built on a foundation of Mach and lived to tell, it was originated by the OSF. That was the group that opposed AT&T & Sun's System V R4 collaboration and sought to build their own commercial version of Unix.
Digital paired it with their smoking fast Alpha hardware, where it earned a significant reputation as a blazing combination, and as a leader in 64-bit computing; when Compaq bought Digital, they renamed it Tru64 to highlight this. The use of Mach was no certainly issue for the administrators of big iron who run Tru64.
Instead, it was assassinated in its prime. After HP bought Compaq in 2001, CEO Carly Fiorina bet the company on HP-UX and the promises of Intel's soon to fail Itanium. While she focused on grooming herself for political ambitions, Fiorina managed to slash and burn the technology portfolio of the once inventive HP, and had anything from Compaq shot in the face.
As part of her reign of terror, and much to the disdain of its users, Fiorina wrote off Compaq's Tru64, the Alpha processor (which was the fastest on Earth at the time), and many of HP's employees. Shortly afterward, she got canned and left the smoking ruins of HP behind as a devastated shell of its former self. Tru64 is now on life support from HP through 2011.
More Nails in the Coffin
So there you have it: Linux would make a really bad kernel for Mac OS X. It would turn the Mac development world upside down unnecessarily, and there's nothing inherently bad about Mach anyway. The people who talk about how XNU is inherently several times slower than Linux are either uninformed, liars or idiots.
Apple has better things to do than chase fleeting buzz. The XNU kernel works. Sure, there's plenty of room for optimization throughout Mac OS X, as there is with any software product. In that regard, Apple can import technology from the various BSDs, each with its different focus. In contrast, Linux has one codebase, and a general focus that isn't closely aligned with Apple's.
Of course, Mac OS X already benefits from a lot of software designed for Linux. It can borrow ideas from Linux, Solaris or elsewhere. Mach provides XNU with a competitive advantage in its unique design. It's investable. Apple's intending to build for 15 years on Mac OS X, and they're comfortable with the foundation they've designed.
The next time you read rampant speculation about how Apple is poised to replace their languishing kernel, you can consider the flippancy of such writers who speculate how Apple will ditch their kernel for Linux in one article, and how they should be chasing an even more extreme and experimental microkernel core in the next.
Like it, hate it, have a correction? Leave a comment! - Daniel Eran