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How OS X Executes Applications
MacHore writes "0xFE has an excellent tutorial on Mach-O, which is the file format used by OS X executable files and libraries. It goes into great detail about how Mach-O works, and explains what OS X actually does when it loads and runs an application. Subtopics include Universal Binaries, The Dynamic Linker, Using otool, and other goodies."
A lot of that has to do not only with Mach, but simply with the fact that up until recently, a lot of OSX applications (specifically, those built on Carbon) were not multithreaded. In other words, if one bit of the application hangs or times out, the application and everything that depends on it goes to hell.
This is why BeOS appeared to be lightning fast on even slow machines. Even the smallest tasks were executed independently, and bottlenecks were hardly noticiable.
Apple's doing a good job making everything work, and Cocoa is definitely a step in the right direction, but apple really needs to kill all of the single-threaded applications they've got now. The Finder is the most prolific and outrageous example of this, and anybody who's ever lost a network connection while a network share was mounted knows what I'm talking about (the system virtually hangs for 45 seconds until the connection times out. awful. simply awful)
Otherwise, I love OSX.
-- If you try to fail and succeed, which have you done? - Uli's moose