Although Apple has been mum on many of the details of Leopard, CEO Steve Jobs did preview some of the coming attractions back in August. This month, I'm looking at another of those new features in Leopard that has gotten a lot of attention -- and engendered a fair amount of informed speculation -- among Mac fans: Spaces.

What is Spaces?

Simply put, Spaces creates virtual desktops. A virtual desktop acts like an imaginary second display, allowing you to position a number of windows among various virtual desktops. You can also switch between them, in effect turning your head to look at a different "physical" screen.

As with using multiple displays, the advantage of virtual desktops is that you can organize the various applications and windows that are displayed at any given time without closing them or minimizing them to the dock. You can still have windows from a dozen applications open -- but you're not distracted by all of them overlapping each other. Of course, virtual desktops are much less expensive than purchasing multiple displays (which isn't really an option at all when you're working on a MacBook in a coffee shop or library).

For example, if you're a graphic design student, you might be in the college library with your MacBook working on a project with multiple Photoshop, Illustrator, Word and Quark windows all open at the same time. You might also have iChat and Mail open, too. And if you've got headphones with you, chances are that iTunes is running. That's a lot of windows for a single 13.3-in. screen. Enter Spaces, which allows you to group together all of the windows related to your school projects on one virtual screen, or Space, and have another screen for e-mail, iChat and iTunes. Even better, you can create a different Space for each project -- or piece of a project -- you're working on, perhaps using Spaces to group all of your Photoshop and Illustrator windows together while keeping the Quark and Word windows for text and layout apart.

All Spaces will have the same resolution or screen size, which is determined by the display settings for your computer. If you change the display resolution of your computer, each Space will be affected, too.

Switching between Spaces

Apple's design of Spaces makes switching between each one very simple. You can click the F8 key (a hot key that can be changed in System Preferences if your F8 is otherwise in use) to display a virtual map of your various Spaces and then select the one you want with the mouse. (It's much like the way Expose allows you to see all of your open windows and then select one). You can also press the command/Apple key and one of the four arrow keys. That allows you to switch to whichever Space is "next" to the one your using. The arrows correspond to the virtual map of the Spaces you've created. When you press the F8 key, you can even drag individual spaces around to reconfigure the virtual map.

Not only can you rearrange Spaces while viewing this virtual map, you can easily drag windows from one space to another. In the earlier example, you might opt to drag a Photoshop window into the same Space as a Quark document. That way you could see how well the image you're working with fits with other elements on a page. This also reflects another point: Spaces are as much about organizing windows as applications -- an application can have multiple windows in different Spaces. Not surprisingly, this ease of interaction between Spaces is one area where Apple has excelled in designing the usability of a virtual desktop solution.

What about the finder, dock, Expose and application switching?

In designing Spaces, Apple had to make choices about how various standard OS features would interact with multiple virtual desktops. The first of these features is the dock. Apple could have chosen to display the dock in only one Space (much as it's displayed with multiple physical displays). Or it could have displayed it in each Space, showing only the applications running in that Space. It wisely chose neither approach. Instead, it made the dock display consistent in each space -- meaning that it looks identical in every Space, with all running applications shown, regardless of which particular Space contains the windows for that application.

When you select an application -- either from the dock or by using the application switcher key combination (command/Apple-tab) -- whose front-most window is in a different Space than the one you're currently using, you will automatically be switched to the appropriate Space. It's a little unclear how Leopard will determine which window is front-most if an application contains windows in multiple spaces. It seems logical that the most recently used window will be selected, much as the application switcher always displays the most recently used application as the next choice. But for those kinds of details, we'll have to wait on Jobs and company for more information.