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The Family Tree

Although this document covers the basic concepts in bringing UNIX applications to Mac OS X, it is by no means comprehensive. This section is provided to give you a hint on where to look for additional documentation by outlining how Mac OS X came to be. Knowing a little about the lineage of Mac OS X will help you to find more resources as the need arises.

In this section:

• BSD
• Mach
• NEXTSTEP
• Earlier Version of the Mac OS

• BSD

Part of the history of Mac OS X goes back to Berkeley Software Distributions (BSD) UNIX of the late seventies and early eighties. Specifically, it is based in part on BSD 4.4 Lite. On a system level, many of the design decisions are made to align with BSD-style UNIX systems. Most libraries and utilities are from FreeBSD (http://www.freebsd.org/), but some are derived from NetBSD (http://www.netbsd.org/). For future development, Mac OS X has adopted FreeBSD as a reference code base for BSD technology. Work is ongoing to more closely synchronize all BSD tools and libraries with the FreeBSD-stable branch..

• Mach

Although Mac OS X must credit BSD for most of the underlying levels of the operating system, Mac OS X also owes a major debt to Mach. The kernel is heavily influenced in its design philosophy by Carnegie Mellon’s Mach project. The kernel is not a pure microkernel implementation, since the address space is shared with the BSD portion of the kernel and the I/O Kit.

• NEXTSTEP

In figuring out what makes Mac OS X tick, it is important to recognize the influences of NEXTSTEP and OPENSTEP in its design. Apple’s acquisition of NeXT in 1997 was a major key in bringing Mac OS X from the drawing board into reality. Many parts of Mac OS X of interest to UNIX developers are enhancements and offshoots of the technology present in NEXTSTEP. From the file system layer to the executable format and from the high-level Cocoa API to the kernel itself, the lineage of Mac OS X as a descendant of NEXTSTEP is evident.

• Earlier Version of the Mac OS

Although it shares its name with earlier versions of the Mac OS, Mac OS X is a fundamentally new operating system. This does not mean that all that went before has been left out. Mac OS X still includes many of the features that Mac OS 9 and earlier versions included. Although your initial port to Mac OS X may not use any of the features inherited from Mac OS 9, as you enhance the application, you might take advantage of some of the features provided by technologies like ColorSync or the Carbon APIs. Mac OS 9 is also the source of much of the terminology used in Mac OS X.

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