Chapter 6: User Interfaces for Mobile Media 223 several selections on and off independently. Mode switching is per- formed via a menu item, or the user may press down another key to enter in multi-select mode. 6.3.4 UI Structure and Navigation Graphical user interfaces for desktop computers, such as Apple MacOS or Microsoft Windows, provide application windows. These windows divide the screen into regions containing application-specifi c informa- tion and controls; the user can also switch between the open windows to change the active task quickly and easily. Displaying several overlap- ping and resizable windows at the same time requires a large display in terms of physical display area and pixel resolution. Since mobile devices have small screens, presenting multiple windows in a similar manner is problematic. First, the controls needed for window manipulation, such as borders and a title bar, consume screen real estate. Second, as mobile devices rarely have continuous pointing devices, direct window manipulation and moving between windows is diffi cult and slow. Therefore, instead of using the term application window, Symbian OS-based Series 60 UI refers to an application view as a collection of user interface components that the application requires. The screen layout is divided into regions for dedicated purposes. The topmost region, the status pane, presents the status of an applica- tion and/or the device; the main pane, at the centre, contains the application data; and the navigation pane at the bottom displays softkey labels, as shown in Figure 6-5 (Symbian 2005). Since available screen space is at a premium, mobile devices cannot present information in a parallel manner. For instance, an MP3 player fi rst shows all available artists in one view. After selecting an artist, the user moves to another view that presents all albums by the selected artist. Then, once the desired album is selected, the user is able to browse the tracks, once again in another view. The example above illustrates sequential information presentation, where the views are separated and the user must make a selection before moving to the next view. A sequential displaying of views forms a hierarchical tree, where the user moves (navigates) between nodes that present the views, some- times called “states”. Figure 6-6 shows an example of an overall navi- gation structure of a hypothetical MP3 player. The fi rst state becomes active after the device’s power has been turned on, and thus it is often called the idle or main state. From the idle state, the user can enter into one of the three states that are descendants of the idle state (Music library, MP3 player, or Settings); each of them has further sub-states.