A Bit of Geek Talk

So far, in this chapter, everything is fairly simple, but Mac OS X isn’t only about its Finder windows and applications. In fact, the most important changes are under the hood. If you don’t speak geek, don’t worry; this section is for those who do understand these complicated words and who will appreciate reading some of the nitty-gritty that goes on behind the scenes.

Mac OS X offers preemptive multitasking, which is a way of allowing applications to work simultaneously and share processor time. Previous versions of Mac OS—from System 7 on— used cooperative multitasking, where each application would cooperate, but only one could use the processor. All active applications and processes had to share the processor, kind of like time-sharing a vacation home. When things worked fine, you wouldn’t notice that this was a problem, but when poorly written applications got confused, the entire operating system could freeze or crash.

Mac OS X freezes rarely and crashes even less frequently. One reason for this is its protected memory, which prevents applications from intruding on other applications’ memory locations. While individual applications can freeze, you can force them to quit (see Chapter 13), and the operating system remains unscathed. You’ll never see the kind of problems that occurred with Mac OS 9 or earlier, where several extensions could cause conflicts, causing the operating system to be unstable.

Under Mac OS 9 and earlier, you could run out of memory if you opened too many applications. Each program was allocated a certain amount of memory when it launched and, if you needed more, you were out of luck. Mac OS X uses dynamic memory allocation to ensure that applications only use memory when they need it. You no longer set an amount of memory that an application uses or adjust virtual memory settings; Mac OS X handles all of this.

Another way Mac OS X lets you work more efficiently is through multithreading; a thread is an active process run by an application or the operating system. Together with preemptive multitasking, this allows many applications to work at the same time, smoothly, without one application slowing down the entire system.

Finally, the stability of Mac OS X is due in part to its foundation: Mac OS X is built on top of a FreeBSD Unix system, one of the most stable versions of Unix available. While most users will never see this underlying system, power users who want to access the command line and make low-level changes to the way the system works will be delighted to have a venerable foundation for Mac OS X.