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Chapter 4. Programs and Documents > The "Heads-Up" Program Switcher

4.2. The "Heads-Up" Program Switcher

Only one program can be in front, or active, at a time.

To make a different program active, you could simply repeat the technique you used to launch the program initially. Click its Dock icon, double-click a document icon, or whatever.

You can also switch to a different program by clicking its icon on the Dock. Doing so makes the program, along with any of its open windows and toolbars, pop to the front.

But Panther introduces a faster, more direct program-switching feature—faster, because you perform it entirely from the keyboard. Just hold down the key and begin tapping the Tab key (Figure 4-3).

In fact, you can use this feature in three different ways, all of which are well worth learning:

When Programs Are Actually Folders

You may have noticed that Mac OS X programs don't seem to have 50,000 support files strewn across your hard drive. To open AOL, you no longer need to first open an America Online folder; you can just double-click the AOL icon itself. That's a much better arrangement than in Mac OS 9 or Windows, where many programs must remain in special folders, surrounded by libraries, dictionaries, foreign language components, and other support files and folders.

The question is: Where did all those support files go?

Mac OS X features something called packages or bundles, which are folders that behave like single files. Every properly written Mac OS X program looks like a single, doubleclickable application icon. Yet to the Mac, it's actually a folder that contains both the actual application icon and all of its hidden support files. (Even documents can be packages, including iDVD project files and some TextEdit documents.)

If you'd like to prove this to yourself, try this experiment. Choose Go→Applications. See the Calculator program? Control-click it. From the contextual menu, choose Show Package Contents. You're asking Mac OS X to show you what's inside the Calculator "application icon" folder.

The Calculator package window opens, revealing a Contents folder that you've never seen before. If you open this folder, you'll find a handful of strange-looking, Unix-named folders and files that are, behind the scenes, pieces of the Calculator program itself.

The application-as-folder trick is convenient for you, of course, because it means that you're generally free to move the application to a different window—or uninstall the program by dragging this single icon to the Trash—without worrying that you're leaving behind its entourage of support files. It's also convenient for programmers, because they can update certain aspects of their applications just by replacing one of these component files, without having to rewrite the entire program.

You can even try out this programmery benefit for yourself. In the case of the Calculator and many other Mac OS X programs, the Resources folder contains individual graphics file—PDF or TIFF files— that serve as the graphic elements that you see when using the program. For example, the file lcd.tiff in the calculator's Resources folder contains the image of the calculator's screen (where the numbers appear as you punch the calculator number buttons).

Using a graphics program, you can change the background of this light-yellow calculator screen to, say, light blue. The next time you double-click the Calculator—which you now realize is actually a folder behind the scenes—you'll see your modified calculator design.

  • If you keep the key pressed, each press of the Tab key highlights the Dock icon of another program, in left-to-right Dock order. Release both keys when you reach the one you want. Mac OS X brings the corresponding program to the front. (To move backward through the open programs, press Shift--Tab.)

Figure 4-3. Apple calls this Windowslike row of open program icons a "heads-up display," partly because it's translucent (like the projected "heads-up display" data screens on a Navy jet windshield) and partly because you don't have to look down to the Dock to see what you're doing. (Shown here superimposed on another window to illustrate its translucence.)

  • If you leave the key pressed, you can choose a program by clicking its icon with your mouse.

  • A single press of -Tab takes you to the program you used most recently, and another press returns you to the program you started in.

Imagine that, for example, you're doing a lot of switching between two programs—your Web browser and your email program, for example. If you have five other programs open, you don't waste your time -Tabbing your way through all open programs just to "get back" to your Web browser.

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