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Mac OS X and Darwin

The word Darwin is often used to refer to the underpinnings of Mac OS X. In fact, in some circles Mac OS X itself is rarely mentioned at all. It is important to understand the distinction between the two—how they are related and how they differ.

Darwin is the core of the Mac OS X operating system. Although Darwin can stand alone as an independent operating system, it includes only a subset of the features available in Mac OS X. Figure 1-1 shows how Darwin is related to Mac OS X as a whole.

Darwin is an open source project. With it, you as a developer gain access to the foundation of Mac OS X. Its openness also allows you to submit changes that you think should be reflected in Mac OS X as a whole. Darwin has been released as a separate project that runs on PowerPC-based Macintosh computers as well as x86-compatible computers. Although it could be considered a standalone operating system in its own right, many of the fundamental design decisions of Darwin are governed by its being embedded within Mac OS X. In bringing your applications to the platform, you should target Mac OS X version 10.1.4 (Darwin 5.4) or later.

Mac OS X itself is not an Open Source project. As you can see from Figure 1-1, there are many parts of Mac OS X that are not included in the Open Source Darwin components. Part of your job while porting is deciding where your application will fit in Mac OS X.

If you are a developer whose tool is a command-line tool (or has a useful subset that is a command-line tool), you can, of course, simply port your application as a command-line tool or service, which is usually not that complicated. By doing this you gain a small benefit, in that it is now available to Mac OS X users who are familiar with the UNIX command-line environment. You will not be able to market it to Mac OS X users as a whole though, since many users do not even know how to access the command line on their computers.

The basic steps in porting a UNIX application to Mac OS X typically include:

1. Port to the command line.

2. Provide a graphical user interface (GUI).

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