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Overview of Mac OS X

Mac OS X is a modern operating system that combines the power and stability of UNIX-based operating systems with the simplicity and elegance of the Macintosh. For years, power users and developers have recognized the strengths of UNIX and its offshoots. While UNIX-based operating systems are indispensable to developers and power users, consumers have rarely been able to enjoy their benefits because of the perceived complexity. Instead consumers have lived with a generation of desktop computers that could only hope to achieve the strengths that UNIX-based operating systems have had from the beginning.

This chapter is for anyone interested in an overview of Mac OS X—its lineage and its open source core, called Darwin. Here you will find background information about Mac OS X and how your application fits in.

In this section:

The Family Tree
Mac OS X and Darwin
What Macintosh Users Expect

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.

• 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.

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).

What Macintosh Users Expect

In bringing your UNIX application to Mac OS X, you are entering a world where great emphasis is placed on user interactions. This brings you many opportunities and benefits as a developer, but also some responsibilities.

Benefits of Porting to Mac OS X

Porting to Mac OS X has three primary benefits:

• stable long-term customer base

• good inroad into education

• powerful developer tools

Bringing UNIX applications to Mac OS X can be very profitable if done correctly. Well-designed Macintosh applications of years past are the standards of today. PhotoShop, Illustrator, and Excel are all applications that first made their name on the Macintosh. Now is the time to win the hearts of Macintosh users with the next great application. In a word, possibly millions of paying customers!

Macintosh users are willing to spend their money on great applications because they know that Apple strives to give them a high-quality user environment. Apple developers are known for providing great applications for that environment.

For years, Apple has been known for its commitment to education. Mac OS X targets the education market for developers and is an ideal platform for learning for students. With its standards-based technologies as well as home-grown technologies, you have an ideal platform for use in educational application deployment and development.

Mac OS X also provides benefits in a development environment. Apple strives for standards first, then it adds that little bit that makes it better on a Mac. As a developer, you have access to many of the development tools and environments that you have on other platforms, like Java, OpenGL, POSIX libraries, and the BSD TCP/IP stack, but you also have built-in benefits like the Apache Web server on every computer, the Cocoa object-oriented development environment, a PDF-based display system (Quartz), Kerberos, QuickTime, a dynamic core audio implementation, and a suite of world-class developer tools. By adding a native Mac OS X front end to your application, you can achieve a cost-effective new deployment platform with minimal additional development effort.

Mac OS X adds tremendous value both to you and your customers on a standards-based operating system.

Responsibilities of Porting to Mac OS X

Along with benefits come responsibilities. If you have decided to make a full-featured Mac OS X application, here are some guidelines to keep in mind.

• A Mac OS X user should never have to resort to the command line to perform any task in an application with a graphical user interface. This is especially important to remember since the BSD user environment may not even be installed on a user’s system. The libraries and kernel environment are of course there by default, but the tools may not be.

• If you are making graphical design decisions, you need to become familiar with the Apple Human Interface Guidelines, available from the Apple developer website. These are the standards that Macintosh users expect their applications to live up to. Well-behaved applications from Apple and third-party developers give the Macintosh its reputation as the most usable interface on the planet.

The responsibilities boil down to striving for an excellent product from a user’s perspective. Mac OS X gives you the tools to make your applications shine.

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