The Macintosh started out with a single-tasking operating system that allowed simple switching between applications through an application called the Finder. More recent versions of Mac OS have supported multiple applications running simultaneously , but it wasn't until the landmark release of Mac OS X that true multitasking arrived in the Macintosh world. With Mac OS X, Macintosh applications run in separate memory areas; the Mac is a true multiuser system that also finally includes proper file-level security.
To accomplish these improvements, Mac OS X made the jump from a proprietary underlying operating environment to Unix. Mac OS X is built on top of Darwin, a version of Unix based on BSD 4.4 Lite, FreeBSD, NetBSD, and the Mach microkernel .
Unix itself was invented more than 30 years ago for scientific and professional users who wanted a very powerful and flexible OS. It has evolved since then through a remarkably circuitous path , with stops at Bell Telephone Labs, UC Berkeley, research centers in Australia and Europe, and the U.S. Department of Defense Advanced Research Projects Agency (for funding). Because Unix was designed for experts, it can be a bit overwhelming at first. But after you get the basics (from this book!), you'll start to appreciate some of the reasons to use Unix:
It comes with a huge number of powerful application programs. You can get many others for free on the Internet. (The Fink project, available from SourceForge (http://fink. sourceforge .net/), brings many open source packages to Mac OS X.) You can thus do much more at a much lower cost. Another place to explore is the cool DarwinPorts project, where a dedicated team of software developers are creating Darwin versions of many popular Unix apps (http://www.opendarwin.org/projects/darwinports).
Not only are the applications often free, but so are some Unix (and Unix-compatible) operating systems. Linux and FreeBSD are good examples. Like the free applications, most free Unix versions are of excellent quality. They're maintained by volunteer programmers and corporations who want a powerful OS and are frustrated by the slow, bug-ridden OS development at some big software companies. Mac OS X's Darwin core is a free Unix OS (get it at http://developer.apple.com/darwin/), but it does not have Mac OS X's easy-to-use interface. Many people use Mac OS X daily without ever knowing about all the power lurking under the hood.
Unix runs on almost any kind of computer, from tiny embedded systems to giant supercomputers. After you read this book, you'll not only know all about Darwin, but you'll also be ready to use many other kinds of Unix-based computers without learning a new OS for each one.
In general, Unix ( especially without a windowing system) is less resource intensive than other major operating systems. For instance, Linux will run happily on an old system with an Intel 80386 microprocessor and let multiple users share the same computer. (Don't bother trying to use the latest versions of Microsoft Windows on a system that's more than a few years old!) If you need a windowing system, Unix lets you choose from modern feature-rich interfaces as well as from simple ones that need much less system power. Anyone with limited resources ”educational institutions, organizations in developing countries , and so on ”can use Unix to do more with less.
Much of the Internet's development was done on Unix systems. Many Internet web sites and service providers use Unix because it's so flexible and inexpensive. With powerful hardware, Unix really shines.