CHAPTER 9 Darwin and the Window Server If your only previous exposure to computing is to previous versions of the Macintosh operating system (Mac OS) or Microsoft Windows, you've probably noticed that Mac OS X is very different indeed. If you're familiar with the "classic" Mac OS, you've prob- ably noticed that with Mac OS X you don't need to preallocate how much memory a program uses, and that programs in the background run without any noticeable deg- radation in performance. If you have used either Mac OS or Windows, you've surely noticed that Mac OS X does not crash as much as these other operating systems -- in fact, for most users it doesn't crash at all! In this chapter, we'll see why Mac OS X is so different.