Mac OS X v10.4 "Tiger" and the Power of UNIX
The most widely-sold UNIX-based operating system, Mac OS X offers a unique combination of technical elements to the discerning geek, such as fine-grained multithreading, Mach 3.0 microkernel, FreeBSD services, tight hardware integration and SMP-safe drivers, as well as zero configuration networking. Tiger's state-of-the-art kernel features improved SMP scalability and 64-bit virtual memory, while standards-based access control lists take UNIX permissions to the next level.
Even better, all the UNIX technology in Mac OS X (aka "Darwin") is Open Source so you can download it for free, examine it, and modify it directly. If you are interested in learning more about the UNIX underpinnings of Mac OS X, as a developer or administator, please visit the Open Source topic page.
For existing UNIX developers, the X11 windowing system is built-in to Mac OS X (as an optional installation). This windowing system is used by many existing UNIX applications to draw windows, controls, and other elements of a graphical user interface. The Mac OS X implementation of X11 is integrated with the Quartz drawing environment to give applications a native Mac OS X feel. This integration also makes it possible to display X11 windows alongside windows from native applications written in Carbon and Cocoa.
For More Information