OS X Mountain Lion Bible

Managing Multiple Open Applications

OS X has preemptive multi-tasking, which means the operating system can run more than one process (such as an application or various functions within an application) at a time, in a way in which OS X dynamically parcels out chunks of time to the various open application processes so no one process can hog all the resources.

In practice, this means you can have multiple applications running and switch among them easily. But the ability to run multiple programs at once can be disorienting. A stray mouse click or gesture can take you from one program to another, bringing its windows to the front and putting the application you were working on to the back. To a complete newcomer, it may appear as if a program has disappeared completely, leaving you confused. Of course, most computer users these days are familiar with the concept of using multiple programs at once, and OS X makes the process as straightforward as possible. Even so, you must get used to having multiple layers of programs and documents open at once; these can lie on top of each other on the desktop, like different paper documents lying on top of each other on your desk.

Fortunately, OS X provides many methods to switch among documents and applications. And OS X features such as Mission Control, App Exposé, and Spaces (covered in Chapter 2) offer you a quick means to organize and access documents and applications on your Mac. Mission Control, for example, lets you see all open applications ...