Icon bar
The icon bar is a fundamental feature of the graphical user interface of Acorn Computers' RISC OS operating system. It provides access to all parts of the computer that a typical user will require, and will usually be their starting point for interacting with the system once it has finished booting.
Appearance and features
The bar is fixed in height and located at the bottom of the screen. It takes up the full width of the screen, and a single row of icons is displayed within. Icons are either justified to the left or the right edge of the screen, at the control of the owning program. According to Acorn's official RISC OS Style Guide, a program should place its icons to the left hand side of the icon bar if they relate to physical devices or resources such as filing systems. These will have an item of text underneath them identifying the device or resource. All other icons should be placed on the right of the bar. If too many icons are present to be displayed at once then the icon bar will extend horizontally and become wider than the screen; in order to access the non-visible icons the user must scroll the bar by hovering the mouse pointer at the appropriate edge of the screen.
The result of clicking the left mouse button (known as the Select button) on an icon will vary depending on what the icon represents. For filing systems, a filer window will open containing the contents of the root directory. For document-oriented applications supporting multiple open documents, clicking Select will open a window containing a new, empty document. This is different to the behaviour of the typical Taskbar and Dock, where clicking an icon will result in a task switch (All windows associated with the icon will be brought to the front of the window stack and will gain input focus). For programs that do not support multiple open documents, clicking its icon will typically result in the task switch behaviour.
By pressing the middle (Menu) mouse button while the pointer is over an icon, a context-sensitive menu associated with that icon will open. Although the owner of the icon is responsible for the contents of the menu, the menus for icons with similar functions will typically contain the same subset of options. For example filing systems will allow the naming and formatting of disks, as well as an option to open a window displaying free space. Most applications will provide access to an Info window (displaying the version number and copyright information), online help, and a quit option.
Even if there are no running applications or active filing systems, the icon bar will contain a small number of system-managed icons:
- The Apps icon, located within the left-hand group of icons. This was introduced in RISC OS 3 as a way to access the applications built into the computer's ROM. It is actually just a frontend to the read-only ResourceFS filing system; when the icon is clicked it opens the Resources:$.Apps folder. Although ResourceFS is read-only via the usual filing system interface, system APIs can be used to add or replace files. In RISC OS 3.5 this functionality was leveraged to allow the user to easily add his own applications to the Apps folder, via the AddApp[1][2] star command. The applications inserted using AddApp are simple shell applications that will just execute the real, original copy of the application when they are started. This allows the applications to be added without using significant amounts of |RAM and restricting them to read-only access to their internal files.
- The Task Manager icon, located to the far right of the icon bar. When clicked with the left mouse button this opens a window similar to that of the Windows Task Manager, where the running programs and processes are listed, along with their memory usage. Basic control over the processes is also available (forced termination and in some cases manual control over how much memory is allocated). From the task manager's icon bar menu it is also possible to shutdown the computer, exit the window manager to the single-tasking CLI, or open a multi-tasking CLI window. A desktop boot file can also be saved, which contains the current state of the desktop and any loaded programs. In theory this provides full hibernation support, although in reality because each program is responsible for saving and restoring its state within the file, the computer's state after executing the saved boot file will not be identical to its state before.
- The Display Manager icon is located just to the left of the task manager. This allows selection of which display mode is in use. In versions of RISC OS prior to 3.5, where memory restrictions forced most people to use modes with 16 or less colours, it was also possible to alter the current palette from this icon.
In RISC OS 3 the AddTinyDir[1][2] star command was introduced, which allows an icon for any folder or application to be added to the left-hand side of the icon bar. This provides functionality similar to that later embodied in the Mac OS X dock.
History and evolution
Arthur
The icon bar first appeared in Acorn's Arthur operating system, in 1987. There was no task manager icon on the right of this icon bar, only one to exit the system. Another significant difference between this icon bar and that of the versions from RISC OS 2 onwards is its appearance, which was reflective of the operating system as a whole.
RISC OS 2
The appearance of the icon bar changed in 1988 when RISC OS 2 was released. In this version of the icon bar, the task manager appeared on the far right of the bar, with the palette icon immediately to its right. The task manager's icon is based on the logo Acorn used for its Archimedes range of computers. A suite of applications were supplied with RISC OS 2 on floppy disk, and amongst these was one called TinyDirs. This program allowed users to dock applications and directories on the icon bar for convenient access.
RISC OS 3
The RISC OS 3 icon bar appeared in 1991. The basic appearance of this icon bar is the same as it is for RISC OS 2, but with two significant differences; the task manager icon is no longer based on the Archimedes logo, and the Apps icon, providing access to the ROM based applications, has appeared on the left. Another significant change is that the supplied applications no longer include TinyDirs because the AddTinyDir star command now provides similar functionality.