How closely are Mac OS X and BSD related?
I read that Mac OS X and bsd are related. How closely are they related. Can Mac OS X software be tweaked and installed on BSD?
Answer
Back in the days of OS X 10.4 I spent some time failing to write a VFS for OS X. In those days, of the major subsystems of the kernel, only the network stack and the VFS were still truly BSD. At that time, even the VFS had been partly rewritten to make it more modular (all the BSD VFS data structures became opaque pointers and the API was through what were called KPI functions). I believe the network stack was going the same way. There was also a thin layer at the interface with userland that made the OS look like BSD to userland programs.
Everything else had been pretty much rewritten or replaced: memory management, process management etc came from the Mach microkernel; the device driver subsystem was written from the ground up by Apple.
In terms of userland programming, OS X is very similar to BSD and programs written for BSD should be easily portable. However, OS X has a lot of APIs that aren't available in BSD. These include almost everything to do with the user interface - graphics, sound etc. There are also other interfaces that don't exist in BSD such as the launch API which is the OS X preferred way of launching background processes.